This forum post has links to where to turn for support for problems with the Windows edition of Assassin's Creed Unity. Also, a post on the Assassin's Creed Unity Forums from Ubisoft addresses AMD owners playing the just-released stealth/assassination sequel (thanks IGN), explaining what's being done about some of the reported issues on their systems:

We are aware that the graphics performance of Assassin’s Creed Unity on PC may be adversely affected by certain AMD CPU and GPU configurations. This should not affect the vast majority of PC players, but rest assured that AMD and Ubisoft are continuing to work together closely to resolve the issue, and will provide more information as soon as it is available.