Dreamation is my favorite convention but that's mainly because many friends in the RPG design scene travel all over the world to be there BUT they aren't there to sell games, just have fun. I see them at Gen Con as well but they are usually busy selling. Dreamation attracts many people who love independent games as well as popular traditional games. For example, for every awesome cutting edge self published game, you have excellent Call of Cthulhu scenarios. Dreamation is also fantastic for LARPs.
I don't know how big it is, but between 700-1,000 would be my guess. It's a little spread out, so sometimes different types of gamers feel isolated from each other but not as bad as bigger conventions. The hotel that hosts Dreamation is amazing. There is a movie theater built right into the hotel with plenty of varied and good food options near by. The rooms are affordable and a few blocks from the train to and from Manhattan.
Woah, sounds awesome! And yes, very helpful. Too bad about the segregation but I want to haul over from the LARP section to where the tabletops are going on if I'm not too wiped from GMing . Thanks so much for the breakdown... sounds like an awesome con.