The Samsung Galaxy S2 is a fantastic phone. But the Bloatware that comes with it from Samsung totally ruins it. I am not sure what the business justification of literally killing the phone is.
With the original configuration the S2 did not last more than half a day on a full battery charge. And I am an aggressive user in any case.
I recently rooted the phone and flashed the Siyah kernel and Resurrection Remix ROM on to it. The charge now lasts close to 24 hours. That's with my usage. I'm sure it will last more with less aggressive usage.
Kudos to android for being so flexible.