At DEFCON there's a wall with a projection of username and passwords (some of the password that is). When you use any wireless here, it's safe to assume that all the packets are being captured and if you're foolish, you logged in to webmail, pop, AIM, etc...DEFCON is reality concentrated in to one spot- when you see your friend's password on the wall, and a big sheep go by, it's a clever reminder.
This one too:
One the coolest projects I've seen so far at DEFCON was the kegbot, a linux based keg that dispenses beer as long as you have an iButton key. The system keeps track of who you are, how much you're drinking and in team mode- where you rank. the Kegbot crew built and deployed a kegbot on site at DEFCON, we were lucky enough to get there and document the building of it!