An impressive application for two way TV on IP was demonstrated by Italian company, Digital Magics Group at PICNIC last week.
It's a system that enables on-air contributions from viewers via webcam. This opens up all kinds of opportunities from ad hoc chat shows to karaoke.
Technically, not rocket science, but as ever with technology, it was the way that it was implemented and packaged that was impressive.
Expect your 15 minutes of fame any day now (but remember to buy that webcam first).