I have HD with Comcast. I am in McKinney, was one of the early adopters and had my install last November. I would have to rate the service as very good from a quality view point. I did have some initial problems that were resolved when a Comcast tech changed a bunch of connectors, splitters in my cable wiring. HDTV seems to require that you have very good lines and connectors, especially if you have multiple TVs and hence splitters. Service has been great since then.
We get ABC, CBS, NBC FOX (480p widescreen), ESPNHD. Premium movie chanels available are SHO, HBO, STZ and MAX.
The audio for a lot of programming is 2 channel dolby surround. Do get full Dobly 5.1 on many ABC programs, some CBS and some movies.
Bottom line is I would recommend the service. Lack of HD channels is about the only downside right now.
The stb is the Mot DCT5100. They are adding DVR at the end February, which will be the Mot DCT 6204 (I think).
You may also want to check this forum which has some active topics for Comcast in dallas:http://www.dslreports.com/forum/catv