Purchased the pn50c450 last week at Best Buy. I'll give a quick run over my thoughts and touch upon some of the main concerns I'm seeing on the board.
There is a "screen door effect" at close viewing, no question. I step back to 6-8 feet and I can't see it. I view from 10-12 feet in my den normally. I do wear eye glasses; my eyesight is not 20/20, but I can't imagine SDE on this set will be a problem at normal viewing distances for the vast majority of people.
Picture is top notch in my opinion for this price range. Picture adjustments are robust (white balance, gamma, cell lighting, black level adjustments). I'm not sure what is typical on higher end sets, but there are plenty of picture tweaks for my taste. Best Buy had the Samsung 1080p step up model side with the c450 and I could not see justification for the price difference with regards to picture quality, albeit comparisons were done on in-store settings. I could tell at 6 feet and less that lettering on the 1080 set had a smoother edge. Take a step or two back and the difference was virtually imperceptible. I'm not sure what additional feature set you get with the step up model, other than 1080p. I believe the price difference was near $500. Not worth it IMO.
My set does "buzz", slightly. You can hear it on mute if you put your ear up to the TV; at 6-8 feet, it disappears to my ear. It is not by any means bothersome to me. I would classify it as typical electronics noise, nothing more.
Stand does not swivel, and TV is not particularly sturdy (wobbles at slightest touch). It is not unsturdy to the point I worry about tipping, but with a 1 year old, I keep her away (not that I wouldn't anyway). It comes with a cord you can fasten to the TV and attach to the wall (which I have not done). Screws that attach the stand are difficult to line up and don't want to go in. I had this problem in set up, and have seen several other reviews that noted the same thing. Stand is not a long term issue, however, as it will be mounted on my wall shortly.
Screen is very reflective IMO. Not mirror like, but close. The 1080p set looked to have less reflection in the store than the 720p. My den has below average sunlight, so it is not a huge problem for me. All the light comes from behind the TV, but I still get some reflection during the day. If you have a windows across from your set or your room gets alot of light, you may want to look elsewhere.
Remote is not very responsive. Have to point it directly at the TV. Not backlit, but didn't expect it to be at this price range.
Despite some qualms, I am very satisfied with the set, other than one flaw which I hope is not a widespread problem with the model. While watching hours of NCAA bball this past weekend on CBS, I noticed frequent judder in commercials and periodically in live action. It was easy to notice in the commercials, as they repeat the same commercials over and over, and it would judder (looks like a frame skip) in the same place every time they aired. I have noticed this on both CBS and NBC broadcasts, but have not had one problem on Fox or ABC. I receive over the air signals with an antenna, but it is not a signal issue. The commercials are the easiest comparison, because certain ones judder in the same spot everytime on CBS and NBC, but are smooth on Fox and ABC. CBS and NBC both broadcast in 1080i, while Fox and ABC broadcast in 720p. Could the scaling mechanism in my set be defective? It doesn't appear to be handling the 1080i signal well. Has anyone else had a problem? I've posted this on other sites and have had no feedback. Best Buy and Samsung were no help. I'm leaning towards returning it for another set, and would like to get another C450. I just don't want to get another one home and have the same problem again. Feedback is much appreciated. Thanks.