MY Touch Pro 2 on Sprint has also been having this problem (SOD or Standby of Death) just in the past few days. Stock rom, even reset it all back just like the day I got it.

First a tip, if your phone is doing this you can wake it up by calling it from another phone. Saves you the long soft reset time if you have another phone handy.

Anyway the problem is Gmail. They must have changed something since it seems rather widespread.

The simple fix is to change the schedule for any gmail accounts to be manual. If it does it automatically at all it will lock up eventually.

If you check a gmail account manually and it hangs on "connecting" or "disconnecting" (IIRC) then you need to kill it from your task manager. It only happens sporadically. Anyway I think that when this hang happens in the background (via scheduled email checking) then that causes the SOD. If you get a manual check to hang it does not cause the SOD, but you'll be draining your battery if you don't kill it.

Anyway, I hope there will be a fix at some point, but this workaround at least makes the phone usable again.