I always found it weird to hear people say things like "My friend asked me to come" (with no prior mention of said friend), as opposed to "A friend of mine asked me to come". To me it seems as though the former would imply that the speaker has just one friend. I think this usage is well widespread though, but is there any concern about its correctness?
I don't see a similar pattern in use for words other than "friend" (perhaps for family members such as "brother" as well?). Correct me if I'm wrong, but I think "You can read about that in my book" would be an unusual thing to say if I'm the author of several books on the same subject matter, unless the particular book I'm referring to is clear in context.