I'm torn... in the first month of usage, I didn't even rack up 900 megs on 3G. I use my iPad mostly at home and at work, where I have wifi. Mostly, the 3G is used in my car, and I am obviously not streaming videos while I'm driving. However, I often use the map program as I am driving... even if I don't need it. It is fun to play with at stoplights. I also frequently stream radio programs over 3G while driving.
With my type of usage, I'd find it pretty hard to reach 2gb in a month. I guess there are people who stream a lot of videos from non-wifi locations.
Anyway, I am torn between downgrading to the $25/2gb and saving $60 a year, or keeping the unlimited plan just in case. The only time I couls imagine going over my 2gb is if I was taking a road trip and my wife was watching movies in the car. She usually wants to watch the scenery, though (something a lot of today's kids never get to see).