DC is pretty awesome.
Great, varied nightlife: Young professionals party a lot here.
Great food.
Conducive to people with active lifestyles : lot's of parks.
A lot of schools nearby - Goergetown, George Mason, American, Catholic, Howard, etc.
Very diverse: almost nobody is a local (by which I mean from DC, montgomery county, pg county, NoVA).
It's not so big you get overwhelmed, it's not so small you get bored.
Personally, I think it's a great city tobegin professional life after ungergrad/graduate school, work for 3-5 years, move somewhere bigger/flashier (NYC, abroad), and move back to settle (though I'd rather not).