Well, ever since upgrading I haven't come across a game where my computer couldn't handle both. Not even Crysis. So it does get a little annoying.
I mean Jesus... I can play stuff like Mirrors Edge and Resident Evil 5 with 16x AA and the framerate never drops under 60 fps.
EDIT: Heh. Turns out you CAN force AA using the STALKER profile or something. I'll try to figure it out.