Facebook games - I've played console games for over 25 years, and have been playing some Facebook games for about 2 years now. I play Mafia Wars, CSI, and just started Assassin's Creed. For me it's a time kill as I do other things. I don't ever spend any money to get an advantage in the game, though Zygna certainly makes it very, very easy to do so if you want.
I'll never give up the traditional games, but I do agree that it would be really neat to expand some of the types of facebook games out there. You see Ubisoft and CSI attempting to tie in the console/PC game to their facebook game, and I'm looking forward to seeing how that works out. I think this is an area that could expand rapidly and turn into something really cool.