I flash twice my Xperia U to ICS and I done it well. At frist one, i made without reset factory and the second one with reset factory.
In both cases I got the same problem.
The ICS is draining battery life hard, even in stand by. No ...
Calm down guys. Just wait.
Official announcement from Sony Ericsson about 2011 line will receive Android 4.0 ICS.