Like many people, I jailbroke my 3G out of curiosity. I didn't find anything useful or interesting enough to keep my phone that way, so I restored my phone to factory default settings. I did notice though, that if the battery percentage display was enabled (via sbsettings or bossprefs) while jailbroken, it will remain enabled through a factory reset.
To disable, I had to re-jailbreak the phone, hide the battery percentage display, back up via iTunes, then un-jailbreak (incarcerate?), and restore from backup.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090803132516587