No guys, this is not funny anymore. Reboots are also present in newer 4.0.4 stock rom. Look in a google, there is a lot of complains about this proble, even on new Xoom 2. Still no solution except sending tablets back to the company.
I noticed that tablet performance slows down during usage, than it just freezes and reboots. Gonna try to disable multitasking in dev menu. If someone resolved this problem, please let us know.