I think it's gotten to the point where it's foolish to buy a larger, more expensive TV that's not HDTV compatible. Prices are falling fast, too - I read an article somewhere that HD sets should fall another 40% in the next year. HD Tivo is out there, too, but I'd wait on that a while...
I have DirecTV with the HD subscription and view HD over-the-air a lot, too, with a $20 antenna. I can switch between the OTA HD broadcast and the standard DirecTV to compare and there is absolutely no comparison (I watch mostly sports). Seriously - it makes me wonder how I ever enjoyed watching anything before... HD really is spectacular and guests notice it without any prompting... football games are very popular at my place
That said, not all HD viewing looks the same... depends on every link in the chain... for example, I've read that satellite HD transmissions are often compressed whereas OTA transmissions are not... anyway, good luck...