I still don't understand how you can get 3 days from a 3GS Although mine is generally searching for signal and gets used very heavily. Plus I always have GPS, WiFi and BT running as well as other things.
I *can* get 3 days from it. Normally, I don't like it getting too low, in case I'm stranded with a low battery. It was fully charged before I left for Oxford meet yesterday, and I suspect I'll pop it on charge when I get in the office tomorrow morning. As an estimate, it'll be around 40%.
Wifi/BT/3G/GPS always enabled (although latter isn't constantly used, although most apps have permission to use Location Services). Wifi at home, and work. Not sure if Wifi is kinder than cellular data. Had mega life in Cyprus with BT and Data disabled, think I only charged it once in the week
I have, as previously eluded to, noticed a massive, massive difference between my NiffNaff SIM and Vodafone SIM. Voda struggles to last the day, due to poor signal. I guess with Voda, its constantly trying to reach the unreachable network.