I usually use WiFi, rarely use 3G but today my electric was off so had to use 3G, my battery was dead by 2pm with light use, On WiFi the battery is at about 30% by bedtime.

It definitely uses more, especially if the signal is low. That's why on some phones like iPhone there's a setting to turn off 3G.

If you are on Android there are numerous widgets you can download to toggle it on/off.

Ive only done this occasionally when I really need to conserve battery life.