From my experience, when I connect to the internet through 3G, even if I don't have IM, email or any program who uses internet connections on the background, I still get about 6/7 hours of battery. If I connect to the internet only when I need it, I can have 2 days of (moderate use) battery. Some of my friends have Android devices (HTC Magic and Nexus one) which opens IMAP IDLE connections and are constantly connected to IM through 3G and their batteries last for a day, which leads me to the conclusion that currently maemo isn't performing much power saving when connected to internet through 3G. I expect PR1.2 brings some good improvements on this area.