After two weeks with my new iPhone 3G I agree with other commentators about the limited battery life. A day out and about and I'm down to the last 10% of power. In fairness to Apple, the iPhone is just so handy and useful that I am using it for far longer than any previous phone or PDA. It's a fully-fledged computer, not just a phone. And my old Treo 750 wasn't much better on battery life if I'm being honest.
I am currently testing an auxilliary battery which plugs into the iPhone and can give up to two full charges. The small and neat Power Monkey, which looks nothing like a monkey, is proving to be a valuable addition to my portable arsenal. There are a number of similar devices such as the 3GJuice and the Kensington but on paper the Power monkey has the highest power capacity. It is British designed and you can see details at PowerTraveller UK.
Although the monkey is expensive at £65 it does come with an array of connectors for many mobile devices and a quality carry case. A bonus is a solar-panel charger so, in theory, you can have power wherever you go. I won't hold my breath for solar charging performance in Britain, but I am looking forward to trying out the device when I get back to Athens in October.