Been twice, although both times were in Milwaukee. The thought of a Gen Con without a visit to The Safe House just doesn't seem right.
Now, the last time I was there was in 2000, but I was amazed at how approachable all the companies were, even the (at the time) big guns like TSR and FASA. You could just walk up and chat with Dave Arneson or Steve Jackson. Granted, that's just good PR, but to react enthusiastically to what had to be thousands of variations on "And then my character..." they heard that weekend required the patience of a saint. And if you came at them with something that was actually original or unique, their eyes lit up and they started jabbering away just like any other geek.
And while I never went to one, I hear the annual White Wolf party is the stuff of legend.