Here's a good example. When I take this quiz (or any other like it), I invariably get Philadelphia if it's an option. Otherwise, it's Northeast or Mid-Atlantic. However, people here in Southern California almost never can guess my hometown by accent (attitude maybe, not accent), and native Philadelphians don't think I have their accent or any real accent at all. Perhaps it's from an expensive education just far enough outside of the city, or from my voracious media consumption.
Results: What American accent do you have?