I actually watched a movie on Vudu this weekend in HD. I was expecting it to be not much better than the SD version, but I was pleasantly surprised. The movie wasn't what I would expect from HD DVD or Blu-Ray, but it was reasonably close to what I expect from DirecTV. It's pretty astonishing such quality can be streamed from the internet so rapidly. It will only get better.
Yeah. I tried streaming a few clips on my Apple TV with the latest firmware and the quality is pretty good considering its all going over the internet.