I have Charter Cable here in CA, and they just rolled out HD here. For an extra couple of bucks a month, they replaced my Digital Scientific Atlanta cable box with an HDTV-capable box. The HD is great -- looks awesome and sounds awesome with the 5.1, but the programming selection leaves much to be desired.
Currently they're only offering HBO HD and Showtime HD -- all of the local stations that broadcast HD at different frequencies are not carried by the cable company. To add insult to injury, the cable box has no antenna input (other than the RF needed to connect Charter's signal) so I can't even hook up an outdoor antenna to capture the other HD programming that's being broadcast in my market.
All in all, I'm glad that I get to use the full capacity of my HDTV without investing in the expensive DirecTV or DishNetwork equipment I'd need to access it from Sat, but I wish I could get more programming choices...hopefully Charter will offer them soon. At the end of the day, it's definitely worth an extra $3 a month though to get the incedible pictures and sound that I get from what programming I can!