With Wifi-on, 3G on, continuously downloading podcasts and web surfing whilst listening to said podcasts over its mono-speaker, I got just over 7hours of battery life before the phone shut itself down :) This is pretty impressive, and certainly explains why I usually get about 2 whole days with moderate use with this phone.
Acer Aspire One (with 9-cell battery):
With wifi-on, screen at 40% brightness and on 'home/office desk" mode, tweetdeck constantly on and itunes downloading podcasts every so often, the battery would last 4 hours and 50 minutes before the netbook would forcibly go into hibernation mode (at 3% battery life). I think this is phenomenal, and infinitely better than the paltry 1hr 30minutes that I used to get when using the supplied (2-cell!!!) battery. Since having the battery, I've found that I'm using the AAO a lot more, and now I'm tempted to get a USB dongle so I can take the web with me :)
Anyhoo, that was all, except that I am interested to find out what the battery life is on the shiney new iPhone 3Gs under the same conditions - I'm interested in getting one, but I have to see whether it can come close to the numbers I'm getting on my current phone, otherwise I could potentially be disappointed.