Okay, just got back from checking out the Vizio P50HDM at Costco, in preparation for a potential purchase of the P42HDTV during the March Madness promotion.
My first impression was that the set design and construction looks better in person than it does in the images I've seen on the net. I didn't get the impression that it was "cheap" just looking at it. As found, the image on the screen was miserable looking. I found the control buttons on the side of the bezel (really liked the quality feel of them, btw) and sussed out the adjustment procedure fairly quickly.
The reason the image quality was so bad was that the saturation, hue, brightness, and contrast, were all maxed to the right!? After 5 minutes of tweaking and fussing, I had achieved what I thought was the optimum settings I could attain with what I know about the set and its root level options. I was satisfied with the results, although there was still a soft fuzziness that I couldn't quite get rid of.
I then compared it to the 50" Panasonic plasma they had around the corner from it (can't remember the model #). The Panny was definitely producing a sharper image, but not $1,000 better, IMO. I also compared it to a 42" Pioneer plasma, and again, give the nod to the Pioneer, but it's 10" smaller and they wanted $200 more for it.
I know we can't quote specific prices here, but the $200 price cut was already in effect for the P50HDM. They had 4 of them on the floor in boxes beneath the display model, but there were no signs of boxes for the P42HDTV. I wanted to ask a clerk, but I never saw one until he caught me off guard looking at a Surround sound system next to the TV section. He came by to thank me for getting such a good picture back on the Vizio! I thought that was pretty cool of him to notice that and go out of his way to tell me that in another dept. I was so shocked by it that I forgot to ask him if they had stock on the 42" sets!

Anyway, many of my fears about the quality of the build of the Vizio have been allayed by this viewing today. I thought the PQ looked better than the Sony, RCA, and Samsung LCD, and DLP rear projections which were nearby for comparison, but it's clearly a step down from the Panny and the Pioneer plasmas. Even at that, I am more than satisfied with the PQ I'd be getting for the price. I just can't justify the price difference between it and the other two brands for what I'd call a 10 to 15% advantage in PQ. I'm also not what most of you would consider to be a true videophile, so I'm easy to please.
Oh, one thing that did bother me a bit... they were showing some previews from what looked like the "Today" show, and I saw some horrific artifacting on the characters faces as they were moving about. I went in and found a motion filter in the Advanced menu, and tweaked it to midscale, but I really didn't know what I was doing. There's also a digital filter there, with which I was unfamiliar, so I left it alone. I never saw any further artifacting during motion, including some on ice hockey footage, so it may have been the quality of that Today preview feed. I have a hunch that I'm going to have issues with the SD quality on any of the HDTV sets though. That's something I need to explore.