My battery lasts 24-36hrs on Wi-Fi (connected, collecting mail every 15 minutes, Skype/GChat for at least half that time, OM-Weather widget running). On GPRS, it lasts maybe 5-6hrs...

I use Titan's Power Kernel and some other tweaks to paging and stuff, and 2g-3g switcher, with PR1.3 (which itself made a huge difference to battery life).