I'd expect most users data usage to slow down over the next couple weeks. Once they get to the point where they aren't touching the iPhone all day and downloading apps since everything in nearly new to them then their usage will go down. My first month with a new device is around 4GB. After that I'm consistently around 2GB.
Nott hat it matters but to anyone be it work at home that you have free WIFI access, if you had the 150mb plan that is grandfathered to anyone that had it can keep it even if you were switched to unlimited, This way you can use your wifi and keep the usage down.
All you have to do if you don't want the unlimited is call VZW and ask them to switch you to the 150mb plan for $15.00.
I got this from a high level manager I spoke to and this is what I am doing for now using wifi at work and home.
Only 11 mb for me so far. I've had an iPod touch for over a year, though, so there's not too much to play with that I haven't already. But I am having a ball with Red Laser - I think I've scanned half the house. :o
I've burned through about 200 minutes since I got it thanks to some work conference calls from home, and the call quality is a million times better than my 9650.