Jack Tretton just announced during the Sony E3 press conference that Assassin's Creed: Brotherhood will not only receive exclusive content on the PS3, but will also receive exclusive access to the game's multiplayer beta. We're not sure what that content will feature, but if we were to wager a guess, we'd say "it includes more things you can stab."
Rather than using money earned to bolster a villa, you'll fix up Rome itself, which will change Ezio's social standing, unlock missions and curry favor with various factions. The release promises collaboration with Da Vinci, Machiavelli, and Caterina Sforza, and describes new "secret weapons." Ubi is throwing in poison darts, parachutes, hidden blades and guns, not to mention an "advanced flying machine" -- which is presumably useful in more than a single mission this time.
Multiplayer -- developed by Ubisoft Annecy, who created the online component of Splinter Cell: Chaos Theory -- is said to feature "multiple authentic character classes" (presumably the characters seen in the gallery below) each of whom will use "signature weapons and killing moves."