So the transition date from analog to digital TV in the US is February 2007 and it's probably a good time to start wondering what the switch means to the ad biz. I'll probably do a more in-depth round-up some time in summer, but here are a few initial pointers:
"For starters, instead of a fixed signal that travels just one way, from the broadcaster to the viewer, the digital format allows for the transmission of a two-way signal. This means that DTV shows can be interactive." -- Zmag.org
"A survey conducted after the Super Bowl [in 2005] by the cable network INHD found that commercials broadcast in HD during the game were the most impactful, and most highly rated with adults who viewed the game in high definition. Much of the interest in HD advertising has focused on the quality of the HD image. Relatively less attention has been paid to the quality and impact of 5.1 audio that is an integral part of HD media." -- FilmCore.net
Also check this primer on HDTV at howstuffworks.com and an official guide to transtion from the FCC.