The video offering proof that the console version of Call of Duty: Modern Warfare 3 supports up to 32-player online matches has been pulled due to a copyright claim from Activision, but that fact alone at least suggests that the leak was legit. The brief clip posted at SFX-360 was taken from the game build that Call of Duty XP attendees will be playing this weekend.
In addition to the video's confirmation of 32-player matches, it also showed what appears to be a new game mode, called Bomb. This could be a mash-up playlist of bomb-based objective modes (ie Search and Destroy, Demolition, Sabotage) or it could be a new mode entirely.
A map list spotted in the clip also reveals the names of 13 of the game's multiplayer locations: Carbon, Coast, Dome, Exchange, Hardhat, Interchange, Lambeth, Meteora, Mogadishu, Paris, Plaza, Radar and Seatown.