I'm using the "3G/2G/Dual Mode" widget to shift the cell phone down to 2G mode most of the time, and that seems to help quite a bit on battery time for me. Then again, I'm kinda used to always keeping my battery powered devices plugged in -- I've got both an old iPhone and an older iPod, so I'm not used to a world where you can replace batteries that no longer hold a charge.

There is a wiki page with tons of power-saving tricks:

http://wiki.maemo.org/Make_your_battery_last_longer