When I saw this thread and saw the number of posts I thought there were simply a lot of local folks and maybe a game day was in order like many of the other metro areas are doing. But alas, after reading this thread I fear we would not be able to figure out which side of the Potomac to meet
It just warms my heart to see how neighborly we are all.
As for the original thread question on places to meet folks?
WotC does hold Card game events. There's one in Lakeforest Mall (Gaithersburg, MD). Not directly metro accessible though metro /bus accessible. Mind you, unless you're going for a specfic event or planning on doing other stuff at the mall, going through the trouble of using metro and bus to get to Lakeforest Mall is not worth the effort if all you're going to do is browse/make one purchase.
There's another one in Columbia Mall but that's beyond metro's reach.
Dream Wizards (Rockville MD). I have not been there since they moved. But they do have a good variety and selection. Admitedly, I never got the warm and fuzzy feeling of interest from the staff there (they are always behind the counter talking among themselves when I'm there and any of the few questions I had were always given short terse responses) I was a regular customer for about 5 years (if not more, with purchases at least once a month if not more). Of course, I have friends that say the staff was always engaging, so it may have just been me or something. I always avoided the crowds at Dream Wizards though (and I've heard it can get packed on certain events!) so I can not say how good of a place it would be to meet new folks in that sort of situation.
Also, check out the Gamers Seeking Gamers forum on these very boards! It does not get a lot of traffic. But I do see a DC area game group posted on there once every while (it would take some regular visits to that forum and patience though -- or start your own post to try and gather people and then figure out specifics later).
http://enworld.cyberstreet.com/forumdisplay.php?s=&forumid=49
The yahoogroup thing (mentioned by someone earlier) is also a good idea. I just don't have any personal experience with that so I can not say.
(again, these are just my personal experiences. YMMV)