It seems as though Ubisoft has learned their lesson from Driver: San Francisco and have decided to get rid of the 'always-on' DRM for Assassin's Creed: Revelations.
When Driver: San Francisco came out on the PC originally, players had to stay online at all times in order to play it. Ubisoft required players to do this in order to lower the amount of losses through piracy.
Studio founder Martin Edmonson stated: "It's just, simply, PC piracy is at the most incredible rates. This game cost a huge amount of money to develop, and it has to be, quite rightly - quite morally correctly - protected."
Assassin's Creed: Revelations will still require you to go online, but only the first time you play the game(for activation purposes). After that, players can happily play the title offline.
By doing this, Ubisoft has said that their piracy losses have gone down significantly and they hope for the same success with the highly anticipated Revelations which releases November 15th.
Source: Rock, Paper, Shotgun