I have the Panasonic TH42PZ800u. I bought it in late 2007... I think.(I'm not going looking for the receipt right now.)

 I have literally thousands of hours of use logged on this TV. It is the center of my home entertainment and used at least 4 to 8 hours a day for at least 2 years.( say 4000 to 6000 hours.) I have not spent the $300 to have it professionally calibrabrated, but I did run the home calibration blu-rays put out by HQV and DVE.

I've made a habbit of running the calibration disks a couple of times a year, and have only had to make one adjustment since purchasing the TV. I had to lower the brightness 1 notch. I believe it went from +16 to +15.(not near the TV for exactly where it is currently set.) I feel this is very good, if not excellent, for the level of use my TV receives. I admit I am not putting a scope on the TV to measure the contrast or brightness, but I cannot report any significant loss of black levels that my eye can detect. My blacks are just as inky as they should be, without losing corresponding detail.

If my TV is indeed losing black level, it will need to be a lot more dramatic a change to be clear enough to make any difference to my viewing. Any of my friends who also have HD TVs still prefer watching movies or sports at my place, because the picture is so good. I regularily get the envious comment, "Why doesn't my TV look like that?"

It could be I don't own one of the affected models. But if you want a real world example of what your panasonic will look like after 2 years of use, I can say I am very happy with what I have. My next TV will definately be another Panasonic.