It's hard to judge my battery life. It seemed really good when I first upgraded from 3G to 4. I did get my i4 right after I moved, where I get basically no signal at home and have to turn wifi on for data. With usually average to mildly heavy usage, some days my battery is just gone, while other days it seems to hardly move, probably due to how hard its trying to find a signal. More often than not, I feel like my battery life is pretty bad though.
As a side note, my 3G (iOS 4.0.1) has it's battery meter stuck at 100%. I never know when it's dying, and restore as new hasn't fixed it.