Several Microsoft employees have been spotted on Xbox Live playing Pimps at Sea (Alpha). When questioned, the players slyly replied, "What's a pimp?"
The obvious explanation is that Halo 3 multiplayer testing has begun, under Bungie's oft-used moniker. In fact, 1UP is "totally 100%" sure of it. As for Joystiq, we're a reserved 99.9% sure -- still holding onto some tiny inkling of hope that Pimps at Sea is indeed Bungie's long-rumored Xbox Live Arcade game.
Update: added screenshot [via flickr].