To sum up the whole novel of Bugzilla thread:

Most of the devices with random reboots have a hardware issue. It's not broken hardware, but the power saving timing tolerance thresholds of the OMAP3 CPU are too wide to handle for recent Linux kernels.

There are two devices out there with OMAP3 and recent Linux kernel, the N900 and the Droid. Both have the same reboot issues.

Now that Nokia identified the bug, they have a fix for the kernel and it will most likely be in the next FW upgrade, since this is a critical issue.
No idea, what the Droid will do, though.