I grew up in a very homogenous suburb, and was quite shocked when I moved to Philadelphia for college and started hearing how many different dialects exist even within one city. My untrained ear could not tell you the difference between a New York or Philadelphia accent, but some of my friends swear they can tell the difference between North and South Philadelphians, and spot someone from Jersey in a syllable. Just recently I moved to San Francisco, and I was shocked to hear several people observe that I had an East Coast accent. Throughout your travels around the country, what observations have you made about the different dialects in America? How do different regions differ in terms of syllable emphasis, sentence construction, or even slang?
You might be interested in The TELSUR Project, which is a high-granularity phonological survey of North American dialects. Note that the information presented on that site is very detailed and highly technical.
In particular, there is an overview of major dialect regions, of which they distinguish five major groups:
The Northeast presents special difficulties, as it has the most diversity of any region, and isn't represented in the regions above. Here is a detail map of Northeast dialect regions.
However, there are a multitude of subtle gradations in these divisions, which can be explored by reading through the materials presented on those sites.
You might also like to look through the Harvard dialect survey results, which plot an enormous number of phonological and lexical differences across the country.
I can't tell apart the various accents, either, other than to know that I'm hearing one.
My one story about dialect differences came shortly after I moved to the Philly area, and happened to mention the 202. The person I was speaking to got inexplicably amused, and brought her friend over and had me repeat what I just said. That was when I learned that putting a definite article before a road number is a left-coast thing. Having grown up next to the 101 and spent many hours so-called driving on the 405, it hadn't occurred to me that this could be a dialect thing.
Pennsylvania Dutch country is interesting to me. Perhaps it was only the first-generation immigrants, but my father has a couple of phrases he used to hear, such as "Throw the cow over the fence some hay", or "Throw me down the stairs my shoes", which are the result of English words with German grammar.
Twenty years ago, I had friends who moved to Pennsylvania Dutch country and they had a baby and when some neighbors came over, they asked, "Is your baby strange?", which meant "Is your baby afraid of being handled by strangers?"
Then there's the whole regional naming/pronunciation of location names. For example, I went to school in Rochester, New York and they have a bunch of crazy city name pronunciations up there. Chili is pronounced with both i's long (Chai lai), Avon, on the other hand, is pronounced with a short a, as in avid, then there's Geneseo (Jen eh see oh), and Lima pronounced a la espanol (Lee ma).