After stumbling across Pirates of the Caribbean last night on ABC, I realized that ABC is one of the channels I get an over the air HDTV signal from, so I switched from my cable input to that. And I have to say, HDTV looks a lot better.
As an aside, I've also been rather impressed by the side-by-side comparisons of DVD versus BluRay at stores like Best Buy and Circuit City. But I'm planning to wait until there's a clear winner in the BluRay versus HD-DVD format war (or players that can handle both formats become cheap) before moving from DVD to a new format.