the problem is sbsettings
i restored two different iphone 3g to 3.0 and on my first iphone i used red snow, sbsettings, and irealsms, the battery would drain crazy fast, openning up cydia, checking for any updates, and it would literally be 1% every few seconds. Left it locked/sleep at work with all the settings turned off, an hour later would discover the battery went down by 5% By the time i got off work it was in the red, never happened before the 3.0 update.
With the first iphone i did a clean restore to 3.0, no jailbreak, and there were no battery issues and everything was fine.
Jailbroke it again, sb settings and without irealsms (irealsms uses mobile substrate so i thought that could be the culprit) but the same battery effect.
A test that I discovered to see if my iphone was plagued with battery problems was making a call with max volume and on speaker. The thing basically drained 1% every 2 seconds, CRAZY
I then used a second iphone that has never been jailbroken and did a restore to 3.0. Redsnowed it, added sbsettings again. Once again there were problems, but mostly for calls, calling someone on speaker killed my battery so quickly i could catch the tears from my eyes. Installed iRealsms, same battery crap. So I removed sbsettings and left irealsms with nothing on cept cydia. Wifi + Push were on, push for beejive, and my battery has been great so far.
Went to work, woke up, took it off the charger, usage 3 hours and 21 minutes of music/reading classics, and in total 4 hours and 53 minutes of standby only at 91% battery.
Compared to my other iphone with sbsettings, i remember it drained 5% every hour of music.
I really do think there are only two solutions:
1. Do a restore and setup as a new iphone (my second iphone, i used my first iphone's backup and no problems from that i guess, since the first was never jailbroken the data never got to create any conflict)
2. DONT INSTALL SBSETTINGS !
even the newest sbsettings has been total crap for me
PS. my battery now with my second iphone, with beejive on, wifi, push notifications, i would be msging people for like 20 minutes and then maybe lose 1%, the battery life is awesome now.