I don't watch blu-ray DVDs or HD cable, so I really couldn't tell ya if 120 is the shit or not, I haven't really inputted something with extremely high quality yet.
But the thing I notice most between TVs at least in the store displays seems to be the way they interpret the images, such as outlining foreground objects to give contrast and add depth, or crisp lines on panning shots where the image tends to shift quickly from one side of the TV to the other.