I also have the same problem. My iPhone 3gs used to be quite good from charging once every 2 days to once a day and now i have to charge every 12 hours or less, if i surf the net.

Usage wise has been around the same since i first bought the phone, except that i have more apps now. Big drop in the battery life since last Sunday. Went for some drinks last nite and battery dropped from 36% to 5% in less than an hour, and that is after i turned off all alerts, location services and quit all background app.

My frind told me that if i jailbreak, the problem will be even worse. Anyone can confirm this?

Maybe i should go back to DIGI to check as my warranty expires next month!