I might as well chime in, although from what has been reported so far as Panasonic's response, it may be useless at this point.,
I too have a 42PHD7UY - ordered from VA as soon as they were available. I too noticed this "bug" that appears just as others have described it - when something bright comes into a dark scene, the black levels, which we are otherwise so proud of and the main reason we bought this plasma over competitors in the first place and have spent hours calibrating down to as close to inky black as possible, suddenly go charcoal gray. Then they switch back. I watched the "Eternal Sunshine of a Spotless Mind" and it happens all over the place, because this kind of scene composition happens frequently.
Also, I too have noticed the blacks get darker and lighter and darker (and lighter again) as one progresses step by step up the picture adjustment.
I chalked it up to not having calibrated something quite right yet, or hit upon a weird combo of settings, or something. But it won't go away, no matter what settings are used. It it is just as others in this thread have described. I don't seem to have the s-video issue, but i don't really use that input at this time.
I am just past the window of 30 days from VA, but I will call them to register my findings anyway.
Good luck to us all - here's hoping (for a miracle) that this could get resolved.