I have the 55GT50 - mine is about 2 weeks old. I'm extremely satisfied with this TV. I'm coming from a Samsung LN46A650, which I was also pretty happy with, but this Panny is obviously better in many ways.
I have thrown the gamut of content at it:
- xbox 360 and about 20 games
- OTA HD and SD
- Sony Blu-ray player with many Blu-rays and DVDs
- Netflix and other channels via Roku and Blu-ray player
- SD Dish Network (just have the cheap family plan for my son)
- Downloaded MKVs and AVIs played over the Xbox360 (I mostly watch UK TV, which I get via torrents from a UK site)
I haven't seen anything that has made me regret my purchase or feel the picture was below the quality I'd expect for this TV. My parents have a Panny TC-P50S30, and this TV is leaps better in PQ and brightness.
My primary concern moving to this TV was gaming. I'm not a huge gamer, but I also would return any TV that didn't satisfy my gaming needs. I've yet to throw a game at it that I felt didn't display and play really well. I have to fire up my copy of Limbo just to see if I experience the problem mentioned above. I played it back when it came out, but that was on my Sammy LCD, of course. Might even have to take the xbox to the Sammy, which has been moved to the basement, to see it on there. I haven't seen anything like what was described in any other game so far.
Oh, there is one thing that kind of cheeses me off. Every time you turn the TV on it displays a "sponsored ad" for 5-10 seconds, which is like a web site banner ad at the bottom of the TV when it displays the "Viera Connect" logo. Seems kind of ridciulous to buy a TV and then have an ad pop up every time you turn it on.