Just wanting to share my experience with the upgrade. It was totally horrible and then super awesome.
1. On GB my phone would have battery for days with light wifi use.
2. I upgraded to the x.211 and my phone was super hot while just sitting on the table. With absolutely no use, the battery would die in 30-60 mins at best from a full charge.
3. I upgraded to the x.215 and the problems only got worse. Phone still hot, battery still dead in 30 mins or less, and now many apps not responding and phone randomly rebooting.
All of this happened while I was using the phone for wifi only because I had not yet activated it to my account. After getting a new SIM and activating the phone to my account, every single issue went away. My phone is now dope as hell and the battery has barely gone down at all throughout the day.
This was after many attempted "fixes", so many hard resets, and a few upgrades/downgrades, etc.
What I attribute this to......
1. The phone has many apps that need to "initialize." From "My Verizon Data" to whatever-the-hell else...these apps were running their asses off. As soon as it was activated, had my contacts in it so the freaking fav widget could stfu, and so on, it was fine.
2. The SIM was bad and could not be activated on the network. The phone was persistently trying to access the SIM to activate the phone. This also killed the bat.
Anywho- If you are not in a 4G area, are using your phone on another network ("flashed phone"), do not have your contacts loaded, have not factory reset, etc., you may have issues.
Try these:
1. If you are on Verizon, make sure that you factory reset your phone and go through that stupid setup process again. DO NOT cancel out of it early.
2. If you are not in a 4G area, or are on another carrier, TURN OFF 4G until you can provision it.
I am loving ICS now....but want JB already. Hell, I have official JB 4.1.2 on my XOOM! Think I may rom this thing until an official drops.
***EDIT***
Forgot to add this. I removed my storage card and did another hard reset just before activating the phone. I noticed this morning when I saw my storage card on the table. I doubt the storage card has anything to do with it, just wanted full disclosure.