Maybe I'm alone in this, but I bought the extended battery two weeks after I got the phone in August and STILL had trouble getting through a day without worrying about charging. After the final Gingerbread update, I've noticed an impressive increase in battery life. At least a 20-30% increase.
I'm now 1 day, 13 hours, 10 minutes on a charge, and I have 19% battery remaining. This is moderate use (probably 3-4 hours of screen time a day, about 20 pictures taken including a few with flash and location awareness on, plus I have all data set to push at default or maximum rates, three weather apps, Google Reader updating in the background, Touchdown and MobileIron running, Facebook and Google+ pushing status updates, Gmail in push, etc etc). I run Google Maps in the foreground with the screen on for my 40-minute round trip to work.
I'm in a 3G-only coverage area, but I have not turned off 4G or done any battery-saving stuff like that.
Stock, running active wallpaper in the background, and Go Launcher.
Two other Thunderbolters at work (both stock battery users) have mentioned a marked increase in battery life after the last Gingerbread update.
I still loves me my extended battery, don't get me wrong - you can have that when you take it from my cold, dead hands. But the last update DID help with battery life for every Thunderbolt owner I know personally. Yes, there are only three of us, but we all have consistent increases in battery life coincident to the last update.