I've seen the problem on my phone... originally I though I had a corrupt SD card, but that's not it. The one posting I saw somewhere that resulted in a response that said "that works" was the one where someone disabled the advanced wifi sleep policy. If you go to Wifi settings to where you view the available networks, and then click on the menu button there is an Advanced option. Under the advanced option you can set the Wi-Fi Sleep Policy to sleep "Never" according to the post I read.
I have no idea whether this works-- I recently did a factory reset for something else, and this always works temporarily to stop the reboots. Can't hurt to try.