I have been suffering from random reboots for several months. The Tivo became almost unusable because it would reboot 9-12 times per day and often cut off recordings.
I thought it was the hard drive so I replaced it. An hour after I replaced the hard drive, I got another reboot and then several more after that.
I know from when I used to use the Tivo wireless adapters that Tivo can be very sensitive when it comes to networking issues. I switched to MoCa several months ago (via Actiontec routers running in bridge mode). I haven't had a problem but I decided to unplug the ethernet cable from the back of the Tivo and see if I still had the reboot problem. It's been over 24 hours and I haven't had a single reboot. Something is happening with the network adapter that Tivo doesn't like. I'm going to swap it out with a different one and see if that fixes the problem. The reboots occur even when I am not actively pulling anything from the internet (I use Standard menus). For those of you still suffering from reboots, you may want to consider your internet connection as a possible problem.