Ran an upconverting Oppo DVD Player (very high reviews) and a PS3 for a while when PS3 first came out. Both DVI (which is same as HDMI without sound, which I run through optical cable) and both through a 1080p 102" screen with a ceiling-mounted DLP projector. The Blu Ray smoked it on a screen that big. Then I got an xBox 360. Moved the Oppo to another room. The HD DVD picture equals the Blu Ray. The on screen menu options, sound, and internet options are better on the xBox. So, I personally wish HD DVD would win. But I’ll deal with whatever happens because I rent with Netflix anyhow so I don’t have a library of useless szhit if one or the other loses.
But all in all, as you get bigger in screen size, there is a noticable difference from an upconverted DVD and a true 1080p HD/BR. Especially on action stuff or CGI or dark sets.
I just hope BR catches up on the web-linked extra stuff and sound options.