Ian (yes, _that_ Ian) linked me to a fabulous page (while he was browsing AVS) that compares HD DVD/Blu-ray content to DVD.  It's a flash app that lets you scroll over the difference between the two.  For those of you that are still skeptical or especially those that don't know the different I highly recommend you check this out.

Note, some items may not load (if the bars stay at 0 for a long time) so simply hit back and try another.

xylon.haloapplications.com

I especially recommend these:
Serenity
Chronicles of Riddick
Stargate
Kingdom of Heaven (warning, looking at this screen difference may result in you purchasing an HDTV and HD DVD and Blu-ray player)

Please be sure to scroll around and look at the picture appropriately.  If the image does not fit on your display then it's probably because your resolution is set to less than HD resolution; if your desktop icons look this good imagine what movies would look like.