Oh god they look bad. Even if you don't force the PS3 to fill the whole screen, the picture quality is borderline unplayable at times. In the past I have had to swap back to a SDTV as this seems to make things a lot better.
Thing is, I can load up any old classic on the PC and simply shove the game into a super high resolution to get an acceptable picture. Why can't the PS3 do this for old PS1 games?