I'm watching store displays as my home TV is 4x3. Anything that's anamorphic, like newer DVDs, comes through properly as long as the DVD player is set right: letterboxed on 4x3 TVs and full screen on 16x9 TVs. Anything which is in 4x3, such as most broadcast TV, comes through full screen on 4x3 TVs and with gray bars on the left and right on a 16x9 TV. Anything that's 16x9 but letterboxed into a 4x3 format, such as a letterboxed VHS tape, a letterboxed movie on TV, or some of the newer TV shows that are recorded in letterbox, will show up properly letterboxed on a 4x3 TV but with both gray bars and black lines on a 16x9 TV.

I've noticed at home that a lot of the TV shows I watch now are being broadcast in letterbox (such as _Angel_ on the WB, for example). I assume that if I had a 16x9 TV that it would put the gray bars on because it's a 4x3 signal, and then show the black lines top and bottom which are part of the signal.