There's a company, miCard.tv, which is working on developing these cards, and the software to go with it. You'll "earn" points for watching channels - or for not fast forwarding through the ad breaks.
Me, I'll stick with my new viewing habits, thanks. What I want, when I want it, and without those tedious mind-numbing commercials.
However it does imply an API which can be used to get additional information out of a TV programmes interactive channels. I wonder if there's something in that which could be used to develop a new generation of interactive TV applications that link digital satellite to media PCs...