I've had my 50" 600U for about a week. At this time I only have a progressive Sony DV DVD player hooked up to component and Radio Shack's top end HDTV indoor antenna that lets me see a few HD and digital TV channels.
I ran the break-in DVD for a few days 24/7 (when I wasn't watching anything) just to play safe.
I haven't got to the last nth in picture tweaking but after using my dated DVE calibration DVD, I generally find that color and tint at 0 are most accurate. Standard mode seems best. Picture is at +20 and Brightness pleasing at +10. Sharpness way down or I see noise. Color Temp at Normal or Warm. Black level at Dark. These will probably change but suit DVDs for the most part.
The HD I've seen is impressive. Hard to find fault there but the jury is out until I get the DISH HD receiver installed.
Some say the new Panasonics have taken a step backward in build quality and PQ. Build quality is a notch down. Especially the remote feels cheaper and is quite weak in communicating with the TV. I think thats inexcusable for any TV, regardless of price but is a sore spot on an item of this ticket.
Several learned members of the forums have judged PQ not as smooth as the previous 500U series. Even Consumer Reports noted picture noise that can't be remedied with any of the settings. I do see something of the like in DVD but not in HD.....yet. I remember being very impressed with the 50U / 500U series in stores. But didn't have the opportunity for a side by side with the 60 / 600Us. Nevertheless, the 60U's I saw were the Belle of the Ball compared to other brands like LG, Samsung, Phillips, Vizo, Maxent, and so on.
The only serious competition comes from NEC and Pioneer at this point. The new Pioneers, such as the 5070 are due about now. Supposedly, price has come down to the Panny point and the've gone a new generation that on paper holds much promise. No one's actually seen or evaluated one. People may hand it the crown or comment that it was better last year.
So, I have 30 days since I bought the set to decide if its a keeper. Ummmm, now its 3 weeks.