I bought my BD player on the same day as my 1080p Plasma. So I never had a chance to see what a non-upconverted DVD looked like on a 1080p display.
That changed this week while I was staying with my in-laws. My dad-in-law had just bought a 1080p but only had a regular DVD player. He hasn't seen the light of Blu-ray yet. (He also argued about how his regular DVDs and his cable channels are in 1080p because the Best Buy sales guy told him so. I tried to explain that having a color TV did not mean he was watching Casablanca in color on it. But that's another story.)
But we popped The Incredibles in for the kids to watch one night.

I couldn't believe how splotchy it was. There were NO straight lines, and everything was just all fuzzy.
It just really showed me how spoiled I'd gotten - even with just regular SD.
Maybe I'll be able to convince him of what he's missing next time he comes to visit US. Then I'll just have to steer him clear of those up-converting HD-DVD players that he can get a great deal on.