It probably drains the battery a little, but doesn't seem to be much. I used to turn off GPS and Wifi/3G depending on exactly what I needed. Now, I've gotten lazy and just leave it all on since the battery lasts all day no matter.
I leave it off until I specifically need it. I got my 3G after the door closed on unlimited plans, don't use that often, just the 250mb so it seems safer to just leave it off.
exactly... when you turn the screen off no more wifi so no push notification no push email... 3G takes over when wifi is off so your always connected...
You always save battery when wifi and 3G is one. It´s not much, but some magazine wrote that you save between 3-5 % when the 3G is off and 4-7 % when the wifi is off. The text is in a foreign language, but you can still check it out about the ipad. And even iLounge has a good test about the battery. Check it out!