The results are in! and well not really much I can say except that Wifi on the iPhone is what kills your battery.

The 3G on/off didn’t make too much difference, I found that although Edge may use less power - it takes so much longer to fetch data that you’re coming out even if not worse. This assumes you even have a 3G signal.

With Wifi turned off I could probably get 2 days out the phone before recharging.

Another tip for saving power - when I call it a night I turn on Airplane mode (disables all comms). I want to sleep not be bugged at night :)