Similar sort of idea to the BBC's iPlayer, but , ATM, it is running on the Mac an Linux as well as the PC, and they are talking to various manufacturers to get it installed on consumer devices.
On top of this, it also allows the user to subscribe to various TV channels, although they currently aren't promising any specific HD stuff.
http://www.synctv.com/
http://www.reghardware.co.uk/2007/11/19/pioneer_synctv/
If it is built into TVs and PVRs/DVDRs, it could be a serious competitor to the established Digital TV systems..