I'm also having the (exact) same problem. I'm using a 450 GTS on 2.6.36-ARCH x86_64 i5-2500 CPU @ 3.30GHz.
From what I've read in all the posts in this thread, the common theme seems to be 64-bit OS+drivers?
My system randomly locks up and can't use X or ssh into the machine. The time before last booting my mouse moved around very slowly and jittery. But the biggest problem is the lockups. For me they occur when I (not everytime):
- start firefox
- play a youtube
- run a console command that generates lots of output
- start minecraft (this one seems to be freezing it every single time now, and it also causes some of the in-game sprites to be spread all across the screen - also across other windows)
I consider myself a more advanced than novice linux user, so perhaps I'll try the kernel debug thing. Don't have a lot of time though.
What I'll also try when I get home is disabling all power management features I can find, as this has helped me with other weird lockup stuff (on a different machine - unrelated).
Hope we can tackle this one, as I am very ready to start enjoying this new system