Via WebWord:

Do You Speak American? is an upcoming documentary about the many dialects that make up American English.

Some interesting observations include:

• Major cities’ dialects are actually diverging, not converging as people predicted with the spread of TV and travel.
• Another “great vowel shift” is underway in the Great Lakes region.
• Most Americans consider the midwest accent closest to “normal” English.
• Southern is the largest dialect group in the country.

And for local flavor, the writeup mentions that they interviewed teenagers in Irvine, obtaining slang terms like “uber” and “tight.”