I was at my dads house yesterday and he has Service Electric Cablevision [ 
Welcome to Service Electric Cablevision ].  I checked out some of the HD channels to see how they  looked, since we don't get them on DirecTV.
DIY HD - Looked just as crystal clear as HGTV.  It was really refreshing to see that program in such pristine quality.
BBCA HD - They were showing some black and white stuff (sherlock  holmes?) and I couldnt really gauge the picture quality.  It looked like  a 35mm transfer to HD, so at least the aspect was good and the clarity  was good considering the age of the material.
Reelz HD - The Kennedies miniseries was crisp with sharp lines and solid color reproduction.  The quality was pretty good.
TruTV HD- 4:3 content stretched to fill the screen.  While it looked  better than TruTV SD, this was not a true 16:9 HD native program.
TCM HD - Really good 35mm transfer of some classic movies.  Filled the  screen and the clarity was outstanding for the era of the content  played.
E! HD - Wow those Kardashians look hot when you can see their pretty  faces in crystal clear HD.  There are a lot of other nice looking woman  on E! all the time.  Good eye candy here.  The cable company had E! in  HD for well over a year or 2.  Not sure why DirecTV doesn't have it.
G4 HD - They had some game show on and the clarity was amazing. 
GSN HD - Black bars on the sides of the screen.  Waste of bandwidth IMO.
PBS Sprout HD - Black bars on the sides, but thinner than the usual  (like when Discovery networks used to slightly enlarge their SD content  so the pillar effect wasn't as bad).
CSPAN2 HD - Bars on the sides with blue graphics and the CSPAN logo.   (Like ESPN puts custom bars on the sides during certain commercials).
NASA HD - Pretty good crystal clear shot of some astronaut interview at the time.
SWRV HD - Crystal clear music videos, but lots of rap and quickly turned it off.
Nat Geo Wild HD - This looked just as good as the regular Nat Geo HD channel.  720p signal.
There were some other channels I couldn't check, like Style and Cooking  HD because they are in a higher package that he does not subscribe.   Overall it was really nice to be able to see these HD channels when  visiting my dad.  The same cable company serves my area, so I'm  contemplating switching in order to get more HD.  The Video on Demand  selection also had quite a few HD movies and also HD content from  Showtime, Starz, ABC, and HGTV.  
I'll give DirecTV the benefit of the doubt, because their software and  equipment is much nicer to use.  So they have some time yet to get the  ball rolling.  But knowing that these HD channels are just a phone call  away is pretty tempting.  I just can't afford to roll with 2 service  providers at the same time.  I know some do it for the sake of Comcast  Sportsnet Philadelphia... but I have other uses for my money.