On the Toshiba set that mastiles linked to a user comments that:
“Although not full HD, 720P instead of 1080 the picture to my eyes looks much better than old 1080”
which is what I was saying about it might be better to buy a 720P set if you watch a fair proportion of SD – you are using the lower resolution of the screen to ‘smooth out’ the ‘upscaled’ SD picture, whereas a 1080P screen will show all the upscaling artifacts in their full glory.
HD broadcasts are 720P or 1080i, so even these will need upscaling to a full HD set.
People always used to praise plasma for giving better pictures, but the early plasmas were ntsc, so 480 lines, and so also did this smoothing.
I had a 540P Sharp which had fantastic PAL pictures from a SCART feed, and it took a tivo type box with 300 mips of power and an hdmi connection to my Sony to only ‘match’ the SD picture quality of the Sharp.