I have had this panel for a few weeks. I had an old SONY HD CRT 34" that broke down and had to replace it. I was sad to see my old CRT go, no 1080p, no HDMI, no smart features at all, but it had a great picture! I replaced it with this and while the picture isn't quite as good, its as good as any flat panel will get to it. I am posting here because, I ordered my 55ST50-2 and then saw this thread and got worried, but now that I have had it for a while I can report that - at least my panel has had virtually no any issues. I say virtually as Ill get to that below.
First off, the picture is great. Great color - except white, but with tweaking it gets almost pure white without affecting the other colors. I have not had it professionally calibrated, its too much for me, but I am a video producer, so I know when color looks off. Without it professionally calibrated, I got it looking up to my standards anyway - which are pretty high.
Image retention has thus far been non-existent. I have had logos, 4:3 content, even a bit of video gaming on it - nothing. Although with gaming I have not played for more than 2 hours, a bit of Uncharted 3, but with the amount of cut scenes etc. I think it helps with the IR issues. I have let my kids watch 4 hours (yea great parent I know) of the same 4:3 show off of Netflix, and nothing happened. A few football games with scores etc. - nothing. However, with the football games during commercials the tickers are gone, so its not really 4 hours straight of football or logos - but again, this is more typical use. CNBC etc with stock tickers during commercials may be an issue if you just leave it on all the time, I don't know and dont feel like tempting fate on that.
The white screen buzzing, I haven't heard it on my panel. I have gone up close and dont hear anything. I admit I have old people hearing buy my wife can hear me fart from upstairs so and hasn't heard anything so... I think I can say that either I fart really loud or its not an issue on my panel.
The only issue I have had is there is a very faint color bleed or halo effect in some shows. I just had to train myself to ignore it - which is hard when you are trained to look for things like that. That said, the rest of the quality is so good that I doubt you will find a panel that has a better picture quality. Every panel I have looked at has had worse issues (uniformity, viewing angles, colors, etc.)
The only major complaint I have is that when viewing Netflix, if the quality changes there is a black frame inserted. Netflix changes quality a lot, so its a lot of flashing black frames. It went away when I had it plugged in wired instead of wireless. Also, and this is just inherent with larger panels, when watching Netflix and its not in HD quallity, you notice it a lot more than you do on your smaller panels
All in all, its a great panel. I cant say that I would go for any other, except to resurrect my old CRT and make it 55 inches and make it 65 lbs instead of 250 lbs.