Sometime back I implemented a Data Usage Calculator on one of our web sites but I never found the time to iron out all the bugs.
Here is a much better one:
http://www.cableone.net/Docs/datacalculator.htmlIt even allows you to change the data "weights" for various activities to tailor it for your estimated use. Very cool.
We send this link to all our potential customers so they can get a feel for how much data they'll need
before they order.