Okay....I got it now
I managed to fix the SD image size problem (I needed to go into the HD box and make some output adjustments) and the ground loop hum (Time Warner had terminate the cable ground at the meter...this was too far away from circuit breaker box -- when I moved the wire to the breaker box, the hum and the screen strobing went away!), so now I am in business.
Okay, so second impressions....
HDTV --absolutely stunning. Major League BB is so clear that it almost hurts. I just turned to a tennis match in HD in INHD, and the match jumped out of the screen.
SDTV -- with the "stretch" function on to make the image fit the screen, the picture is actually not bad at all. Better than on my old rear-projection. At times, for a good feed from a studio setting (e.g. newscast), the picture can border on HD quality.
DVD -- also stunning. I am using my Denon 2910 to upscale to 480p over the DVI connection, and I can't tell if it makes much difference -- but the image is wonderful overall.
Color balance seems dead on -- but I'll get out my calibration disk shortly.
Viewing, even with significant ambient room light, is very, very good. At night, however -- this thing sings!
I love the fact that this set has no speakers and nothing but a thin black plastic frame around the screen -- the image seems to float in the air.
I will keep you posted on my experience. But, at this point, I can say this -- if you're thinking of a 50-inch plasma, think about this one!