I only use wifi at home and find it does no end of harm to my battery life throughout the day if I leave it on. I use SBSettings to quickly turn off the wifi when I'm out of the house but wondered if there was a way to automate this by location or ideally active cell. There is a symbian app which changes nokia profiles in this way: Handy Profiles
If the same app could turn the 3g off when at home, that would be even better!
Agreed using the GPS might be OTT but using "active cell" (as the Nokia software does) would drain no additional battery power and would work just as well for most locations.
From what I understand, "Active Cell" is basically the number given to each mobile areal/mast. Therefore, if you know what cell your are using you can get a pretty good idea of location.