This weekend, that which was prophesised came to pass: Ubisoft´s PC authentication server for Assassin´s Creed 2 crashed, preventing anyone from actually playing the game.
Well, the servers crashed for the whole weekend, leading to this exact situation. A representative for Ubisoft has confirmed that the problem is “unacceptable”, and that a fix is in the works.
However, several enterprising forums are already providing gamers with links to patched executables for the game, thereby rendering the whole DRM point somewhat moot.