I have both a p55st30 and a pn59d7000 sitting in my home right now and I have gone back and forth on these two sets to the point I feel like i am doing TV squats mounting and un-mounting them from the wall.
Both have pros and cons:
The biggest issue I have with the ST30 is that to get it bright you have to bump the back light up to MID in custom mode. Cinema is entirely too dark for my viewing habits. The problem with bumping the back light to mid is the gamma and color accuracy goes crazy. So in it's most accurate mode it does not get very bright 27 fll is what I have been seeing out there.
The PN59d7000 in movie mode (The preferable viewing mode) gets very bright in comparison without sacrificing the image fidelity.
It is nice though to have the ability to get brighter on the ST30 than you can on the d7000.
So unfortunately, to get the st30 bright you have to sacrifice image fidelity. But.....this ability to go brighter is great for gaming or watching anything where you would like it to appear contrasty <-------Not really a word
Overall, the image on the pn59d7000 is smoother and more natural and the colors just look perfect. I don't see the over-saturation of colors on the D7000 I see on the ST30.
This is an AV message board and I have found that I almost wish I never started researching this stuff. What you don't know does not hurt you. Once I started reading the pros and cons of both sets I started looking/hunting for issues rather than enjoying the display. Both have really nice pictures and both have strengths the other does not. The question is, which strengths weigh more in the decision making process. I wish i could answer that for myself. Two weeks to go and one of these sets has to get returned.
Other notes: The ST30 does not buzz at all in my home. Have to literally press your ear to the screen in a silent room to hear it. The D7000 does buzz and it can be heard from my seated position but it is very minimal and less distracting than the fan noise from my ps3 or slim 360
The ST30 has not had any instances of brightness fluctuation. The D7000 has had it multiple times. Not a big deal and not too distracting but it is present. I have tried reseting the TV and adjusting the Eco setting and it did not help. I also compared the exact same scenes where the brightness issues occur on the D7000 and they do not occur on the ST30.
The left speaker has quit working on the ST30 so it is going back anyway.
I am leaning towards keeping the D7000 due to its cleaner image and bright image in the recommending viewing mode. The ST30 is a great set though, good enough for me to go back and forth between the two which is saying a lot considering it is about 700 bucks cheaper than the D7000.