http://www.droidforums.net/forum/dro...t-answers.html

This thread suggests that you turn your WiFi off when you can not use it. It uses some juice if it's on, and if it is doing nothing, that is a waste. When you can use it, it is a batter saver. 3G has to work pretty hard moving large amounts of data, and it is slow, which means it takes longer doing it.

I personally leave my wifi on unless I'm getting low on battery and am away from a charger. At that point I turn off everything I can. It's my only phone, it really does have to be on all the time.