For me, the culprit was Swype.
First week I owned the phone, I got 10 to 12 hours out of extended battery.
Then suddenly the 2nd week, I could only get 4 hours of standby time. (that is charge to 100%, unplug, let it sit on desk idling, 4 hours later it powers off due to low battery).
I started to uninstall apps one at a time, eventually got to swype. after uninstalling swype, I'm now getting around 15 to 20 hours of use out of a full charge on the extended battery.
Just to verify, I reinstalled swype, and sure enough, a full charge died after 4 hours of standby.
For me, 3G vs 4G standby seems to make very little difference in battery run time.
Unlike the Bionic which consumed 4X more power in 4G standby vs 3G standby.
Today's been a busy day at work so I haven't used my phone much. Right now it shows 8.5 hours since unplugging it this morning, and battery is at 83% (extended battery)