I went to PAX East a while back and thought that Stack Exchange would go over very well there.
There are a number of relevant sites that are out of beta - Gaming, Role Playing Games, and Game Development are all spot on and Sci Fi and Fantasy isn't that far out of the ballpark. If you include Beta sites, Board and Card Games would probably be a huge hit, too. And I just happened to wear my Stack Exchange t-shirt one day and met a few Stack Overflow and Programmers users. Given the content and speakers of PAX East 2012, sites like Fitness (there was a panel for fitness and exercise in video games) and Cognitive Sciences (there were at least one or two panels about the psychological aspects of video games, led by researchers) might also serve well from the advertising.
In general, it might be a great place to plug the entire network to a lot of people. We have sites now that cater to the primary focus of PAX, a number of tangential sites, and access to lots of people (who come in from all around the world for this event).
The next PAX East is going to be held on March 22-24, 2013 in Boston (I believe at the Boston Convention and Exhibition Center, where it was held this year). Although there's no information out yet that I can see, since PAX Prime in Seattle is happening next, this is something that perhaps Stack Exchange can keep on the radar. I'm following PAX East happenings, so if there's interest, I can keep the right people up-to-date.