I agree. I'm rolling back to 11.9. My BSOD (on 12.3 and 12.4) shows up overnight while the computer's sitting idle. That machine has a Radeon 4800 in it and pretty much just runs iTunes for the rest of the house. Seems to be only overnight when it happens, so the only activity would be what iTunes is doing in the background (if anything) when nobody's pulling any content around the house. It's always ATIKMPAG.SYS that the BSOD blames.
My gaming rig seems solid on 12.1 (it's a XFX HD 6950 on an i5 2500K), so that does support the theory that something was introduced after 12.1 that is screwing things up.