http://gizmodo.com/5708345/onlive-viewer-for-ipad-introduces-the-unexpected-pleasures-of-video-game-voyeurism
Right now, you can only watch other people play. But imagine, if you will, an eventual controller released for iPad, using Bluetooth, to play games like this...

EDIT: Reading the story a little more carefully, it will be able to play games sometime next year.

This is somewhat interesting. Not really my venue of interest, but I'm looking forward to see how deep this rabbit hole goes.