Consider yourself lucky. My battery is at 85% original calacity and when the charge drops to 30%, odds are about 3:1 that the phone will spontaneusly reboot. When it does, it remains in a boot loop until I put it on a charger or until the battery drains completely, which is usually about 5 minutes. U11 has nothing to do with it though.

I have not noticed any difference in battery drain myself. It has always lasted about a day of my average use (no calls or texts, no 3G, background email check every 30 minutes, some browsing in the evening) - or up to three days if left alone and not used at all.

I do not use the default browser though. There are more usable alternatives. U11 with its icons for bookmarks was the final nail in the coffin.