White screen when loading the game
Andy began playing the game during its midnight launch last night on a 64bit system with a 3.2Ghz i7-950, 6Gb of RAM and a Radeon HD 6890. Initially, he couldn't load the game at all - the game would boot into a white screen and then crash with a Windows error. Fixing this meant updating his graphics drivers - thanks to guide4games.net for the tip. If you do this, try to avoid also installing the latest Catalyst software, as this can cause framerate issues as detailed below.

Persistent framerate problems
Both Andy and I encountered extremely low framerates when playing through the tutorial - 2-5FPS, unplayably bad. Andy's issue may be due to AMD's Catalyst software, which reportedly causes problems in its current version.

In my case, I resolved it by knocking the settings down to their lowest for this opening sequence, in which case I got 25FPS for most of the tutorial and 10-15FPS for a sequence involving cloth physics. This is on a 64bit system with a 3.3Ghz i5, 16Gb of RAM, and a GeForce GTX 560 Ti.