Are you talking 8 hours of uptime or just getting 8 hours total out of your phone? I'm in San Antonio and have had 4G since day 1 and I can still get about 2 days of light use out of my phone with an extended battery.
I got 8 hours of use out of my TBolt yesterday using nothing but 4G...8 hours from unplug to 10% battery left.
Now, I consider my use to be heavy. I sync everything, as often as it can. For instance, if an app can sync once a minute, I set it for that. I use 100% brightness at all times. GPS BT, etc.., on at all times.
I also have ~300 apps installed, so there is a lot to drain the battery. It's just that with 3G, with these same settings, I could get 20 hours if I really tried(just don't use the device as much) 12-15 hours was very normal with 3G with heavy use.
Yesterday, with 4G, I could actually watch the battery drain right before my eyes. Streaming slacker at the gym was great...no stutter or buffering but it used 20% battery in barely a half hour. Basically, 4G has halved my over-all battery life.
On the upside, 20mb downloads is awesome.