News from Google that they are experimenting with contextual TV ads using ambient sound.
This works by having a computer listening to what you're watching on TV and then generating appropriate ads.
This does somewhat presume that:
1) You have your PC and TV in the same room
2) You're not listening to the radio at the same time (you'd be surprised how much people multitask..)
3) You want to leave your computer and its microphone on whilst you're watching telly
4) You want to have Google listening to your front room
I can go on, but I think your get the drift.
Not suprisingly, I think the approach that Adserver takes is far preferrable - by looking at what's being served off the server, using various contextual hooks and then generating targetted ads accordingly.
Narrowstep is well ahead on Google in this regard.