After nearly two weeks with my PN50C590, I haven't noticed any buzzing. There's a low hum if I mute my receiver, but it isn't noticeable with the sound at normal or even low levels. At times there seems to be a bit of noise in the image when up close to the screen (under 1ft away), but that isn't noticeable from my normal sitting distance.
I was a bit paranoid about IR/Burn-in when I first got the set, so I've been trying to baby it a bit. When streaming netflix over the Xbox 360, I noticed that the Netflix logo in the top right corner of the screen (White text/black outline/red background) will stick around for a bit - especially if I'm taking my time browsing movies. But this always goes away pretty quickly. I haven't noticed any other IR issues with XBMC, or TV logos/crawls. I haven't had the chance to play any games yet, but will try to find the time soon - I really want to get back into Mass Effect 2
I did a quick run through the picture settings with a THX DVD I had, and ended up with this:
Picture Mode: Movie
Color Temp: Warm 2
Cell light: 10
Black Tone: Off
Dynamic Contrast: Off
Flesh Tone: Off
Edge Enhancement: Off
Digital NR: Auto
These seemed to look "good enough" for the time being - at least until I get a few more hours on the set. These settings look pretty good at night, but need some adjusting for daylight. I plan to go through this again once I find a bit more time, and hopefully will have something that works better for all lighting conditions soon.
Looking around the net a bit, I found a pretty long review someone wrote up about the PN50C550 on Amazon - Can't post the link yet I guess - just search for the model on their site. Anyway, the reviewer had positive things to say, and posted pretty detailed video settings there. I want to try to personalize my set again myself, but if any of you try these, please share your results.