This bug - occurring when using two nvidia cards with kernel 2.6.32 and driver 195.36.15 (now -24 as well), has now been confirmed by several people. See the updated bug report on launchpad:
This morning I tried also with 195.36.24 (from the x-swat ppa archive), with the same result as with 195.36.15: hard crash around the time X should start, the computer is completely unresponsive (for more than 2 minutes), only a reset allows to reboot.
With kernel 2.6.31-21, it works fine.
I have attached the two bug reports. For both I booted first using the 2.6.32(-21-server) kernel, which led to a crash, and then using the 2.6.31 kernel, which booted fine and allowed to generate the bug report.
The first bug report is when using 195.36.15, the second was made immediately after installing driver 195.36.24.
Note that in the launchpad bug report, all people seem to be using the amd64 architecture so far.