I was flipping around the channels last night and ran into TCM HD for the first time. Although it sounds like the bulk of the movies, if not all, are upconverted to HD, the picture certainly is sharper. If you are an AT&T Uverse customer, be sure to check it out (added to the lineup May 10).
I've seen a handful of true HD classic films, all wide-screen Jimmy Stewart, on HDNet Movies. It'll be interesting to see how this progresses.