Two of my kids have 37inch 720P Vizio LCD's with PS3's connected, and I have a 26inch 720 Sony Bravia with a PS3. The difference between Blu-ray and any other video source is completely visible and totally compelling on these machines.
I also have 2 480i/p machines that I am feeding Blu-ray. The difference is noticeable but not compelling. I do this in order to be able to only buy Blu-ray disks.