I have to say, having the 3G version and using the hell out of it (at least 3 hours a day between commuting and at lunch) and I have had no issues with the battery lasting less than the advertised time. Even with watching movies and surfing nearly the whole time.
When at home I use Wifi and I use wifi when available at lunch, it doesnt matter. I keep the radio I dont use turned off and I keep the screen brightness low unless demoing with photos/video or a few of the "hidden items" games I have. Having the screen at full brightness will drastically reduce the battery life, but that has nothing to do with what radio you are using.
My heaviest day was on a tuesday I was out sick and the WoW servers were down. I used it nearly 11 hours before it started yelling to be plugged in.