If, like me, you're sick of being kicked out of your single player game because Ubisoft's servers are full of fail, there is a solution.
1. Install the game.
2. Let the game and the launcher update by running the game. It may then send you to the login/register screen. Close it.
3. Download this file:
Mirror 1: http://www.megaupload.com/?d=GQ7D7LWI
Mirror 2: http://www.4shared.com/file/5IWlxxTX/AC2Fix.html
4. Go to C:\Program Files\Ubisoft\Ubisoft Game Launcher.
5. Back-up ubiorbitapi_r2.dll, the easiest way is to put it in a zip file.
6. Copy the contents of the zip into the game launcher folder. (If you use AVG turn it off. This is because the dll in the zip is classed as a virus by AVG.)
Just run the game after, you won't need to be online or anything else.