Episode 124 of the Digital Experience podcast, mentioned that Philips has filed a patent that would force users to watch commercials. Essentially, this means that there would be a signal in the video stream, that when sent a TV would prevent you from changing channels. With a PVR, this signal would prevent you from fast forwarding past.
Even if other companies license this technology, I don't think that this will be an effective means for saving advertising. I, as I believe most consumers, would explicitly not buy any TV or PVR that used this technology.