I have absolutely NO idea how much data I use, but I suspect its usually between 1 - 2Gb, but I am unlimited from Verizon, so why do I care? I don't.
I am using the iPhone on Wifi at home and at work, primarily for battery consumption. I like how quick it is to pretty much instantaneously switch back to 3G when I lose signal. On the Droid, I could click a button to turn wi-fi off, but the "handshake" to get it back to 3G didn't always work smoothly, and I sometimes had to reboot the phone. Thus, I was usually hesitant to switch to wifi, just for the possible hassle.
I am using the iPhone on Wifi at home and at work, primarily for battery consumption. I like how quick it is to pretty much instantaneously switch back to 3G when I lose signal. On the Droid, I could click a button to turn wi-fi off, but the "handshake" to get it back to 3G didn't always work smoothly, and I sometimes had to reboot the phone. Thus, I was usually hesitant to switch to wifi, just for the possible hassle.