Would be nice to see an open implementation here. I was kind of thinking that Google Tv might be that. But you really need the ability to overlay the picture. I've considered placing a low resolution lcd next to the telly and doing something myself. Something text based would be fine, it wouldn't need a supercomputer.
When David Cameron visited the Queen to be signed in, I had a live Twitter feed running and it was hilarious. I like the alternative commentary. You could also do audio overlays - over the net. Or even (though a little Orwellian) a webcam to communicate with your mates, something like hangouts.
The smart TV landscape and digital services are pretty confusing. It was tricky enough choosing between Ceefax and Teletext.
Currently I resort to a laptop for lookups and my partner claws her smartphone - which is pretty antisocial, and you miss the action.
