If you bought it in the last 2 weeks, then you get $200 back, I think.
If you bought it before then, you get $100 back: http://www.apple.com/hotnews/openiphoneletter/
I would of been OK even without the $100 refund... I accept that buying the latest technology is expensive. It's just how it works, and I think in the past 2+ months of owning an iPhone, I've gotten my extra money's worth. Still, I'm obviously very glad that Apple decided to do this good-will gesture.