AA and SLI are killing the framerate and mouse movement for me. I'm on an nVidia 7950GX2 though.
Constantly changing the global drivers setup when switching between games is a drag. Forget to change a couple of parameters and it either looks like cr*p or is too choppy. For instance NWN2 needs everything a modern card can offer while SE5 requires "compatibility with the 90's mode". For this the nVidia drivers allow one to create specific profiles for games, so you set it up once for a game and they will always load them when that exe takes over the screen. AFAIK this feature also exists for ATI cards, and a 3rd party utility like ATI Tray Tools may have a better interface for managing these profiles, just like nHancer (
http://nhancer.com) does for nVidia cards.
I remembered this since the other day, after playing NWN2, I launched SE5 when 1.13 came out and got an almost dead mouse again. So I fired up nHancer, created a proper game profile for SE5 after a couple of tries, and can now switch between these games without changing anything in the drivers setup.