[riams]

It lasts a little more than a day, regular usage, not too much gaming. I noticed that the latest 2.3.4 ROM really helped boost battery life.

As a side note: Samsung has released an official 2000mAh battery for the SGS2. It's very reasonably priced here in Sweden, at less than 300 SEK. See: http://forum.xda-developers.com/showthread.php?t=1239719

[flexd]

Nice find! I'm still on 2.3.3 and it says there's no update available yet.

[riams]

You should root and install 2.3.4 via Odin. The battery difference is substantial.