3G network uses a lot more battery of course. Its like throwing a ball. Using a wifi, you need only as much power to throw the ball back and forth to the router, which is a pretty close distance. On 3G, well it requires power enough to throw the ball back and forth between your phone and the cell tower, which could be a mile or so away.
Normally I'd expect the phone to last 4-6hrs of continuous browsing over an internet connection. So basically, if I get 20hrs of standby time (100% to 0%) or 4hrs continous browsing (100% to 0%), if I browse for 1hr, that equates to 5hrs lost in standby time. Are you getting my drift?