I have to say I don’t think there’s a lot of difference between Standard Definition Digital and HD Digital TV- yes, the picture is a bit clearer, but not a huge amount so and certainly not enough to justify the outrageous prices that HD Set Top Boxes are retailing for at the moment.
What is interesting is that, now I have an HD TV, is that my NTSC Adult Swim DVDs from the US aren’t as clear as my PAL Adult Swim DVDs purchased here. There’s not much of a difference, and they still look great on screen, but you can tell which ones are from the US and which ones aren’t.