Well I got my 51" 6900 yesterday and I must say so far I am extremely pleased! The first thing I did was put in my Planet Earth blu-Ray's just to see the diff from my old tv. Let's just say my eyes were getting watery. Some may call me an idiot but I also ended up watching 7 hours of hockey last night and well, zero IR. I am trying to play it safe for the first couple of hours.
As for break in slides, can't I just leave the screen wipe on? It's one big ass greyscale that is constantly moving... :/
Also fun fact I was on my ps3 and I accidentally pressed the left button on the qwerty remote and to my amazement I was able to control the PS3. Was a nice little surprise.
Well back to the main discussion PQ. For me the black levels are surprisingly good and the details in shadows in the darker areas really looked great! One thing I also loved was that on my old set I used to be able to see lines of color lets say in a sky instead of white - blu blending in nicely i would be able to see where each tone starts. On the 6900 this was hardly present, hence my satisfaction.
Buzz? No buzz on my tele, I muted TV nothing, i tried putting vol on TV to max and mute sound system nothing.
Another issue I've heard of was brightness pops. Well During the hockey game I saw maybe one or two POPS in brightness but to me it looked like it was caused more by the CBC cameras then the actual TV.
For my setting I am keeping everything at 50-65 marks for now but when I was watching Planet Earth I figured I'd at least try to see how this baby will look like at my optimal settings. I cranked up the cell light to 17 (huge difference in detail there is much more separation from blacks to white and picture looks much more crispy crunch). The colors as always from Samsung looked (oh em gee) especially the greens.
Umm what else can I add... Oh yea reflections, well I started watching it during the brightest point of the day here in MTL and well it did a really good job of saying "oh no you didunt" to them reflections. yes when screen is off you can see but once you started watching TV its all good in da hood. And when I was watching hockey at night, it was beautiful the border of the TV just melted into the background and all I saw was the glorious 51inch screen.
So yes so far after 7.84 hours of use I am extremely happy with this TV and for the price I mean its a great deal. The TV is also extremely extremely nice design wise! The charcoal finish is astounding especially when compared to ALL of the other TV's I've put up and seen LED LCD PLASMA super hd leoled.... The remote while a bit chunky is nice especially with the added PS3 function.

I still havent played with the greyscale options but when I have the time it will be done! And I wasnt expecting the jump from 42-51 to be that drastic but damn was my head hurting after the first hour. It is all better now and I can now enjoy this TV. So to the guy who has an old 42 inch TV and was in the same boat as I If you see a good deal on this with the 3D goggles go for it!

I will be posting more accurate and detailed impressions once I set up everything nicely, and watch Star Trek.

Just thought I'd share!