It should be repeated that at least the S1 shows a ton of graininess whenever the set is under vivid mode. When I saw the set at Sears I was really disappointed by this graininess and another forum member pointed out that terrible vivid mode. Well I went back and changed the set to cinema and the graininess magically (ok not magically), disappeared.
Of course the problem with plasmas in stores is that they are not bright so the display wasn't as bright and the blacks looked grey. My gf has a plasma though and I can compare to what it looks like in normal indoors lighting and a store. I remember setting the tv to cnet's recommendations and I never touched it after that. I should try vivid mode on it as it's a panny though, just to see the grain.