i dont know if anyone else here knows this, im sure some do, but the Samsung blu ray player, and i think this also goes for the Panasonic that just released, do not accept direct 1080p signals. In other words regardless of if your tv accepts direct 1080p signals through HDMI the player wont output true 1080p. If you have the player set to 1080p in the settings menu what the player does is deinterlace a 1080i signal and convert it to a 1080p signal.
Now to me this doesnt mean a whole lot since i think 1080p isnt the be all end all for high def movies but for all those fanatical people (yes im looking straight at you blu ray fan boys) out there who insist blu ray is heads and shoulders above HD DVD soley based on 1080p support your nuts! Whenever you deinterlace or upconvert an image from 1080i to 1080p you always lose something in the process. Granted it wont harm image quality that you can actually see with the naked eye but still, according to the fan boys its "absolutely neccesary" it be direct and pure.
But i guess its really the only ammo theyve got on HD DVD.