If you are using GPS with maps, that will use quite a bit of power. It will be using GPS, 3G and the screen. Those are the highest battery drains on the device. If you use GPS while driving, I highly recommend using a car charger. Also, have you set the device to CDMA only mode? While in the US, there is no need for it to be in global mode and others report that it helps battery life a lot. I have had it on CDMA mode since day 1, as with all world phones I do that right away.
I charged mine a little while ago when it hit 15% and it had been running for 56 hours. Screen on time was 6 hours 41 minutes. Wifi on the entire time (not connected all the time though, which uses more power) and everything syncing every 30 min (weather, twitter, fb, g+, etc). I also used it for about 2.5 hours of music streaming from google music and about 60 emails and an hour of voice calls.