Never had rebooting issues outside of Navigation
I noticed this problem with Navigation early on in the device when I was still locked and running stock 4.0.2
Near the end of April I was still running stock 4.0.2 and the problem resolved. Not sure if there is an app causing crashing with Navigation?
My phone wasn't particularly hot with reboots either
Now that I'm unlocked, rooted, running a ROM, the issue still has not resurfaced
Maybe check your apps and try deleting some that are unused, maybe there's a conflict among apps? (That's what I did to fix my issue with the device)
I also noticed that when I ran navigation with the screen off (I would keep the screen off for long trips and reactivate it when I got closer and needed the directions), it would be more likely to reboot. I remember only rare reboots with the navigation and screen on at the same time