I received "Superman Returns" from Netflix yesterday. This disc is a HD DVD/DVD combo...HD DVD on one side and a regular DVD on the other. I figured this would be a good disc to test the difference between HD DVD and DVD.
I used my 5 MP Sony CyperShot to capture the images. I captured two scenes from 8 feet away (my normal viewing distance) and the same two scenes from 1 foot away (to better show the detail from HD). My TV set is 46". I did not use zoom for any of the shots. The images were captured in jpeg, so there may be some compression artifacts from my camera that are not in the source material.
The first shot I captured is of a newspaper clipping. I captured this one because of all the small text. Click on these images to see the full resolution...make sure you aren't zoomed out (i.e. should be viewed at 100%) or you won't get the full effect.
This image is from the Superman Returns HD DVD (1080p) on a 46" TV from 8 feet away.
This image is from the Superman Returns DVD (480p) on a 46" TV from 8 feet away.
I am a bit surprised by the results...the images are not that different! HD DVD is a bit sharper, but not significantly.
The next shot is of Lex Luthor in front of a elaborate model train setup. I chose this shot because it has a lot of detail.
This image is from the Superman Returns HD DVD (1080p) on a 46" TV from 8 feet away.
This image is from the Superman Returns DVD (480p) on a 46" TV from 8 feet away.
Same results...the HD DVD is sharper...but not dramatically.
These results are specific to my situation...a 46" TV from 8 feet away. The further you sit or the smaller your set, the less advantage HD DVD has over DVD. The converse is also true...a bigger set or sitting closer will accentuate HD DVD's better image quality. I can't get a bigger TV for quite some time, but I can sit closer. So these next shots are from the same scenes as before, but are from one foot away. At one foot, my camera could only frame a portion of the TV screen. Using the chart at the end of this post, I estimate I would need an 85" TV at my current viewing distance to get the same results as the 1 foot viewing distance with a 46" TV.
These results are from a camera, which does not have the same ability to capture images as the human eye. I can see more of a distinction between HD and SD with my eye than I can with the camera, but these results are at least in the ballpark.
This image is from the Superman Returns HD DVD (1080p) on a 46" TV from 1 foot away.

This image is from the Superman Returns DVD (480p) on a 46" TV from 1 foot away.
At one foot, you can actually see the individual pixels on the LCD display and the black around them (a.k.a. the screen door effect). I can make out some of the article text in the HD DVD, but you can't even read the date/web address in the upper right on the DVD ("Tuesday, February 13th, 2005 www.dailyplanet.com"). Also note the color of the newspaper is more yellow in the DVD and more natural in the HD DVD. Resolution is certainly an important aspect of HD, but the better color reproduction is impressive as well.

This image is from the Superman Returns HD DVD (1080p) on a 46" TV from 1 foot away.
This image is from the Superman Returns DVD (480p) on a 46" TV from 1 foot away.
Look at the lit up windows in the background. There is a clear on/off pattern on the HD DVD, but the windows are just a blur on the DVD.
These photos show how important screen size *AND* viewing distance are for HD content. Here is a good article about this issue. The best part of the article is a viewing distance/TV size/resolution graph, reproduced here because I know I will refer to this quite a bit...