The battery life for me has been great. I was using my phone for about 4 or 5 hours more or less straight yesterday, and when I left, my battery was still over 65%.
With my Nexus S 4G, I made sure to carry around an extra battery because I didn't want it to die and be stuck without a phone, but with this phone, I'm not sure I'll need to worry about until the battery degrades, which will be a while.
The only thing that might change my mind about that is how my usage will change between the Nexus S 4G and this phone. Previously I would use an iPod Touch a lot for work, while my phone would be sitting in Airplane mode on my desk. I'm planning on ditching the iPod Touch all together and using this phone as an all-in-one device. I've yet to test that out at work, but considering my phone will still be in Airplane mode (no signal at work, thanks Sprint. :P) and lasts as long as it does without being in Airplane mode, I'm not sure it will be a problem.