I just got back from Sears and I got a chance to look at the S1 series and I have to say I feel a tad disappointed. Someone else has mentioned that these sets introduce a lot of noise into the picture, and they do!
I noticed this mostly on faces. The S1 was sitting next to an LG plasma and a Sony LCD. The sony had much much deeper blacks but it was experiencing black crush. Curiously, the LG plasma also had a lot of noise in the set but less than the Panasonic. The Sony was very very crisp, you could see a ton of detail on the faces but both plasma's lost a lot of detail to what I would call "white noise". All the tv's at sears were playing the same loop which consisted of a bunch of different things from video games to concerts.
On a bit of a side note, the difference between 1080p and 720p is bigger difference on a 42" set than what most people seem to imply. At about 5 feet back I could tell the difference, but then again, I do like to set close to tvs.