In reply to:

So far, only Discovery Channel, HBO and Showtime have started selling HDTV content to the cable companies. I believe ESPN is joining shortly. Everything else is digital in name only.

Just to clarify, many cable campanies are also carrying the local networks in HD if available. Here in Houston, I believe TWC offers ABC, CBS, NBC, and PBS, as well as Fox (which is only 480p widescreen, not true HD).