I've been twice - this year will be #3.
Both times I had all sorts of big ideas regarding the amount of D+D I was giong to play.
Both times I didn't play much D+D at all.
First one ('03) I got in a 3e game where all the characters were monsters of some sort (I had a lizardman), not much fun. Rest of the time went to Magic, the dealers' hall, the auction store, the art show, killer breakfast, a few board games, and just saying "wow" a lot.
Second time ('09) I ran one D+D game and played in two (one was Jeff Wilder's), the rest of the time went to the dealers' hall, the auction store, the art show, killer breakfast, Braunstein, a few board games, and that damn stupid unsolveable treasure hunt puzzle. Oh, and standing in an overnight line for Magic cards; the only overnight line I've ever done.
This time - well, not sure; other than the dealers' hall, the auction store, the art show, killer breakfast, and trying to meet more of you guys. I'll know more perhaps once the planning forum gets going in here. (hint hint, mods!)
But I do tend to think of GenCon as a D+D-primary event; even if only because when I'm trolling the dealers' hall etc. I'm usually looking for D+D-related stuff.
Lan-"4 nights without sleep, what could possibly go wrong"-efan