i'm an EVO 4g user just waiting to upgrade.

Evo's exprienced the same problems and the only real solution was a bigger battery.

Control your wifi manually when not in use and change your screen brightness. These aare the two biggest energy killers on my EVO.
android phones can benefit greatly from software modification (rooting).

With the bigger battery and brightness setting changes, my EVO went from 12 hours to 2 days with moderate use. I can get a full day with heavy use if I am home and use Wifi.