I didn't factory reset, but I rooted, backed it up (key step!) , then got rid of a lot of the bloatware. Namely car home that always had a service and a lot of other unused default apps. Today my battery has been a champ. Normal use, occasional browsing, and 30 minutes of Listen predownloaded podcast on the way to work. I'm at 79% now after 5 hours off charge.
I did battery calibration too, but not sure ill see its affect until after I do a full discharge cycle.
If you're interested, just search g2x root then g2x bloatware.
Sent from my LG-P999 using XDA App
MyTouch 3G (crusty blood red) - CM6
G2X - Rooted not ROM'd.... yet. -Current device-