Just a few remarks.
I still see this bug with Kernel 3.8, Mesa 9.2.1 and DRI 2.99.904.
Moreover, with switching from Mesa 9.1.x to Mesa 9.2.x the number of lockups highly increased (especially in games).
Additionally with running the latest drivers complete system lockups are gone, but it's still a lockup for multiple seconds with following VT switching.
Maybe these observations help somehow.
Just a few remarks.
I still see this bug with Kernel 3.8, Mesa 9.2.1 and DRI 2.99.904.
Moreover, with switching from Mesa 9.1.x to Mesa 9.2.x the number of lockups highly increased (especially in games).
Additionally with running the latest drivers complete system lockups are gone, but it's still a lockup for multiple seconds with following VT switching.
Maybe these observations help somehow.