The biggest difference between the two forms—and one so obvious that neither of the earlier two answers points it out—is that *proved* is used in the simple past tense, whereas *proven* is not:
>Euclid proved [not proven] the proposition with remarkable economy and rigor.
Another big difference involves the historical status of the two words: For much of the time since 1750, *proven* was far less common than *proved* as a past participle in published works. Here is an Ngram chart plotting instances of "has been proved" (blue line) against instances of "has been proven" (red line) in a Google Books search across the years 1750–2005:
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And here is an Ngram chart of "have been proved" (blue line) matched with "have been proven" (red line) over the same period:
>
In both instances, what had been a very large advantage for "been proved" over "been proven" has melted away—and it bears emphasizing that the results shown here are from (in most cases) copyedited and professionally published writing—not from spoken English.
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***'Proved' versus 'Proven' Through the Years***
Why was "been proved" so much more popular than "been proven" for so long? Its original advantage presumably reflected the preferences then current in spoken English. But starting in the early 1800s, as style and usage guides (and dictionaries) began to proliferate, these authorities began insisting on the rightness of *proved* and the wrongness of *proven*.
One early discussion of popular use of *proven* in North America occurs in John Pickering, [*A Vocabulary, or Collection of Words and Phrases Which Have Been Supposed to Be Peculiar to the United States of America*](http://books.google.com/books?id=EGwPAAAAYAAJ&pg=PA156&dq=%22proven+for+proved+this+is+often+heard%22&hl=en&sa=X&ei=UStYVKqCEtLpoASY2oCADg&ved=0CCUQ6AEwAQ#v=onepage&q=%22proven%20for%20proved%20this%20is%20often%20heard%22&f=false) (1816):
>PROVEN *for* PROVED.
>This is often heard in the debates of Congress, and is sometimes used by *writers* in the *Southern* States ; but it is unknown in New England. "There is (says an English friend) much affectation in the use of the words *proven* and *stricken* among certain American writers and speakers. To labour, as some do, to raise old words from the dead, is not only not *tanti* ; but it shews, that the persons who use these exertions do not consider, that if they are in any degree proper, they ought to be carried out to a much greater extent than the parties seem to be aware of."
But soon enough the usage ceases to be viewed as a charming provincialism and instead receives condemnation as an error. From Joseph Hull, [*Appendix to Lectures on English Grammar](http://books.google.com/books?id=h64XAAAAYAAJ&pg=PP7&dq=%22proven+for+proved%22&hl=en&sa=X&ei=GiJYVKzzC5C5ogSUpoKIBQ&ved=0CEUQ6AEwBzgU#v=onepage&q=%22proven%20for%20proved%22&f=false)* (1828), in the section headed "Vulgarisms":
>*Learnt* for *learned*, and *proven* for *proved*, are common errors.
Seth Hurd, [*A Grammatical Corrector*](http://books.google.com/books?id=BCNAAAAAYAAJ&printsec=frontcover&dq=%22vocabulary%22&hl=en&sa=X&ei=wzNIU6WQB-_lygHd_oGoBg&ved=0CEYQ6AEwBDgy#v=onepage&q=%22proven%22&f=false) (1845) strikes a somewhat conciliatory note, listing *proven* in his section on "Optional Words and Phrases" about which he says, "Being however, somewhat less objectionable than those constituting the body of the work, they have not, like them, been absolutely condemned by the author":
>PROVEN, for *proved*; as "His guilt was clearly *proven*."
And Richard Bache, [*Vulgarisms & Other Errors of Speech*](http://books.google.com/books?id=TQkSAAAAIAAJ&pg=PA81&dq=%22false+collocation%22&hl=en&sa=X&ei=D1QJVNSxKsvloATMioLQDA&ved=0CFMQ6AEwBQ#v=onepage&q=%22proven%22&f=false), second edition (1869), in a chapter titled "Obsolete, Obsolescent, and Local," has this:
>*Proven* for *Proved*. *Proven* does not enjoy the wide use and sanction of good speakers, that should entitle it to take precedence of *proved*. It is used chiefly in Scotland.
>In prose nearly obsolete, but retained by the poets : "When hearts whose truth was *proven*."—Waller
Standing against this tide of opinion is Thomas Lounsbury, [*History of the English Language*](http://books.google.com/books?id=XNU9AAAAYAAJ&pg=PA261&dq=%22proven+for+proved%22&hl=en&sa=X&ei=GiJYVKzzC5C5ogSUpoKIBQ&ved=0CFEQ6AEwCTgU#v=onepage&q=%22proven%20for%20proved%22&f=false) (1879):
>One marked form is, however, here to be noticed : this is the past participle *proven* for *proved*. The word is derived from the French, and in literary use has been inflected, until the present century, like all other foreign verbs, according to the weak conjugation throughout. But the strong participial form *proven* has made its way from the Scottish sub-dialect of the Northern dialect into the language of literature, and not only has grown common, but promises to become universal ; for it is employed by many of the best modern writers, and in particular, occurs frequently in the later poems of Tennyson.
But Luther Townsend, [*The Art of Speech*](http://books.google.com/books?id=4dw9AAAAYAAJ&pg=PA122&dq=%22proven+for+proved%22&hl=en&sa=X&ei=SilYVNzZLtTmoASEkoGICA&ved=0CBwQ6AEwADge#v=onepage&q=%22proven%20for%20proved%22&f=false) (1881) counters by including "*Proven*, for *proved*" in a list of "provincialisms [that] should not be allowed to mar the sentences of any one who aims at correct and chaste speech."
William Hills, [*The Writer*](http://books.google.com/books?id=SJ4nmQL7dFgC&pg=PA168&dq=%22proven+for+proved%22&hl=en&sa=X&ei=GiJYVKzzC5C5ogSUpoKIBQ&ved=0CEoQ6AEwCDgU#v=onepage&q=%22proven%20for%20proved%22&f=false) (November 1908) treats using *proven* for *proved* as an ill-informed attempt at genteelism:
>The misuse of "dove" for "dived," and "proven" for "proved," and "had drank" for "had drunk" is especially common among people who are particular about their language, and who are always careful to say "between you and I."
Frank Vizetelly, [*A Desk-Book of Errors in English*](http://books.google.com/books?id=YrIaAAAAYAAJ&pg=PA178&dq=%22proven+an+irregular+form%22&hl=en&sa=X&ei=tkNYVJv2JYvnoATrg4HYAg&ved=0CB8Q6AEwAA#v=onepage&q=%22proven%20an%20irregular%20form%22&f=false) (1908) concedes a very narrow area of acceptable usage to *proven*:
>**proven :** An irregular form of the past participle of *prove* used correctly only in courts of law. The word should be restricted to the Scotch verdict of "not *proven*," which signifies of a charge that it has neither been proved nor disproved. The modern pernicious tendency among reporters is to use *proven* instead of *proved*.
But Sherwin Cody, [*Standard Test English*](http://books.google.com/books?id=1z7ZAAAAMAAJ&pg=PA94&dq=%22proven+for+proved%22&hl=en&sa=X&ei=rCFYVNqmCoHxoATa74HQDg&ved=0CCoQ6AEwAg#v=onepage&q=%22proven%20for%20proved%22&f=false) (1920) objects to *proven* on very different grounds:
>Avoid *proven* for *proved*, as it is antiquated. Say, He hasn't proved his claim (not "proven his claim").
So, on the one hand (Vizetelly's), usage of *proven* is a modern pernicious tendency among reporters; and on the other (Cody's), it is antiquated.
H. W. Fowler, *A Dictionary of Modern English Usage* (1926) has this advice:
>Except in the phrase *not proven* as a quotation from Scotch law, *proven* is better left alone.
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***More-Recent Views of 'Proved' versus 'Proven'***
Bergan Evans & Cornelia Evans, *A Dictionary of Contemporary American Usage* (1957) try to focus on how *proved* and *proven* were actually being used in 1957:
>**prove.** The past tense is *proved*. The participle is *proven* or *proved*. The participle *proven* is respectable literary English. In the United States it is used more often than the form *proved*. In Great Britain *proved* is used more often and *proven* sounds affected to many people.
And *Webster's Dictionary of English Usage* (1989) offers these remarks:
>**proved, proven** A lot of ink has been devoted to questioning the propriety of *proven* versus *proved* since the controversy started in the 19th century (our earliest comment comes from 1829). ...
>Surveys thirty or forty years ago showed *proved* to be about four times as common as *proven*. But *proven* has caught up in the past twenty years; it is now just about as common as *proved* as part of a verb phrase; it is more common than *proved* when used as an attributive adjective. You can use whichever form you like.
However, Roy Copperud, *American Usage and Style: The Consensus* (1980) sounds a more cautious note:
>**proved, proven.** Four critics [including Theodore Bernstein, *The Careful Writer* (1965) and Wilson Follett, *Modern American Usage* (1966)] and American Heritage [Dictionary] object to *proven* as the past participle of *prove*: "The mine has proven worthless." Three others consider *proved* and *proven* equally acceptable, and both Random House [Dictionary] and [Merriam-]Webster regard *proven* as standard. Opinion is thus divided.
>There is reason to suspect that those who declare for *proved* are taking their cue from Britain. ... Haggling over the propriety of *proven* vs. *proved* in a language like English, which is nothing if not irregular, is surely unreasonable.
William Morris & Mary Morris, *Harper Dictionary of Contemporary Usage* (1985) comes out generally in favor of *proven*:
>**proved/proven** *Proven*, as the past participle of the verb "prove," is not recognized by some linguists. They insist that the past participle is *proved* only.
>...
>Many Americans have shown a preference for *proven*, as in "He has proven to be a valuable worker," and most current dictionaries list *proven* as having equal rank with *proved*, especially when used as an attributive adjective: a *proven* success.
And Kenneth Wilson, *The Columbia Guide to Standard American English* (1993) has this:
>**prove** (*v*.) The principal parts are *prove*, *proved*, and *proved* or *proven*. Both *proved* and *proven* are used not only as past participles but also as participial adjectives [examples omitted]. Generally, *proved* is much more frequent as participle, *proven* more frequent as attributive adjective.
Nevertheless, a couple of high-profile holdouts remain. From Allan Siegal & William G. Connolly, *The New York Times Manual of Style and Usage* (1999):
>**proved, proven.** In general *proved* is preferred: *The prosecutor had proved the defendant's guilt.* But as an adjective before a noun, *proven* is better: *a proven remedy*, *proven oil reserves*.
And from Bryan Garner, [*Garner's Modern American Usage*](http://books.google.com/books?id=Sd3byNeBdR4C&pg=PT2771&dq=%22proven+proved%22&hl=en&sa=X&ei=akxYVNyDBYiuogTat4CQBw&ved=0CBwQ6AEwADgK#v=onepage&q=%22proven%20proved%22&f=false), third edition (2009):
>**proved; proven** *Proved* has long been the preferred past participle of *prove*. But *proven* often ill-advisedly appears [examples omitted].
>In AmE, *proven*, like *stricken*, properly exists only as an adjective [examples omitted].
>*Proven* has survived as a past participle in legal usage in two phrases: first, in the phrase *innocent until proven guilty*; second in the verdict *Not proven*, a jury answer no longer widely used except in Scots law. As for *Not proven*, one writer had defined this verdict as meaning, "Not guilty, but don't do it again."
Realistically, considering that published instances of "have been proven" are approximately equal to instances of "have been proved," Garner's notion that *proven* properly exists only as an adjective seems very difficult to sustain. On the other hand, I'm rather astonished that Mark Mussari, [*The Sonnets*](http://books.google.com/books?id=L7khvtJUmZgC&pg=PT77&dq=%22proven+proved%22&hl=en&sa=X&ei=1FBYVOSTHMHwoATIloHQBw&ved=0CEMQ6AEwBzgy#v=onepage&q=%22proven%20proved%22&f=false) (2010) finds it necessary to translate Shakespeare's use of *proved* (to *proven*) so that a modern audience will recognize what the bard meant to say:
>The speaker closes this sonnet with legal language: "If this be error, and upon me proved, / I never writ, nor no man ever loved." The speaker argues that everything he has said must be proven ("proved") to be an error.
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***'Proved' versus 'Proven' as Adjectives***
As for *proven* versus *proved* as an adjective, here is an Ngram chart for "a proved" (blue line) versus "a proven" (red line) for the years 1750–2005:
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The triumph of "a proven" since about 1960 could hardly be more complete.
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***Concluding Remarks***
It may seem silly to worry about using "has been proven" today, when as many people use that formulation in edited publications as use "has been proved." But it's worth observing that some readers continue to view *proven* as a mistake in that situation—which may or may not matter to you. Once you know the history of the dispute, you can proceed with your eyes open and make an informed decision about which word suits your purpose and your preferences better.