I've lived here about ten years (first five in Northern Virginia, the past five in downtown DC)
Pros:
1.) The tech community here is actually quite good. It definitely feels like it's gotten better since I've lived here. There's no shortage of smart folks working on cool things, even if they are a little more spread out geographically.
2.) While I wouldn't say it's "recession-proof", the area is certainly way less effected by the economy. You can attribute that to the preponderance of government and government-related industries here.
3.) Public transportation is mediocre. Some people think it's great, some people think it's awful. I would say it's somewhere in between. If you live downtown you can get around most places on the Metro. Northern Virginia is accessible out a little ways to Arlington, then it gets sparse.
4.) There's a lot to see downtown if friends or family come to visit. The museums are nice (and free), but I think after a couple months here you'll have had your fill.
5.) You're fairly close to a lot of other places. NYC is a four hour train ride (or a $20 bus ride), Philly is even closer. You have three airports in the immediate area, so you can get to most other places directly.
Cons:
1.) It's really expensive. I moved here from Northern California and was dumbfounded that rent was as expensive here (without the benefit of living near the beach). Like most places, you can find things for cheap if you're willing to commute (or if you live in DC, you can find things for cheap if your willing to live in one of the not-good parts of the city, of which there are many).
2.) Food isn't particularly good. Which isn't to say that there aren't good restaurants, but there's a huge drop-off after you get down from uber-expensive. Oh, and there isn't a single good pizza place in a 30-mile radius of the city.
3.) There is a giant preponderance of government-related folks. This isn't a con for everyone, but anywhere downtown is filled with lobbyists. On a related note, it's also a little weird to live somewhere that is so caught up with politics where your vote doesn't matter (we have no representation in Congress). Local politics is a cesspool, made worse by the fact that DC is cuckolded by Congress.
4.) Some may disagree, but I think the weather here is terrible. It's oppressively hot and humid in the summer (actually four or five months) and then cold and gross in the winter.
5.) If you live in DC, you are relegated to a few neighborhoods that aren't awful. It's changing over time (even just in the time I've lived here), but as to whether that's an improvement is open to debate. If you're talking Northern Virginia, you're pretty much limited to Arlington if you want a semblance of other people. As soon as you start to go west, it's all strip-malls and suburbs.
I've been trying to leave for about nine of the ten years I've lived here, but I know plenty of people who like it here. If you wind up in one of the up-and-coming neighborhoods and meet some good folks, you can enjoy yourself here. Just don't try and look for good pizza.