Upcoming League of Legends-style multiplayer strategy game Prime World to offer gender-based in-game status bonuses (note: link goes to Penny Arcade report, part of the PA conglomerate)
Quick breakdown: if you play a character that is the same male/female gender as in your Facebook profile, and link up with a character/player who is the opposite male/female gender, you both get some kind of bonus. This makes mixed-gender teams more effective and acts as an incentive for male players to bring their "sisters and girlfriends" into the game (because naturally they are not already there, and would be totally into it if only the man in their lives would introduce them).
I don't use Facebook, but I seem to have vague recollections of linking character gender to profile gender being attempted by Facebook game developers in the past. Anyone got any examples and whether or not they ended disastrously?