Welcome to the forum!
The pixelation you noted could be a number of things. For SD channels, some pixelation is normal, since it's upconverting a 480 resolution signal to a 1080 resolution. Think of zooming in too far on a computer picture, and in essence, that's what happens when you're watching SD content on an HDTV. There is some processing that improves the picture already in play, and there's just not much that can be done. That's across all manufacturers, too.
If you're getting the same problem with HD, it could be that you don't have an HD box, or your settings IN the HD box aren't set to 720 resolutions or higher.
You don't have to wait to change the settings. In fact, C|Net has a HDTV Picture Settings Forum, and your particular model has some suggested settings here:
It's a great starting point, and then you can change subtle settings to your taste.
For 4x3 pictures that are NOT sent as a 16x9 aspect from the broadcaster, there may be options in the cable box to automatically fill the screen. Otherwise, it may be something you have to choose, as different signals have different aspect ratios being broadcast. A 4.3 signal could be inside of a 16x9 transmission. (For instance, ESPN can have that 4x3 picture between the ESPN logo on the sides - many broadcasters just leave it blank).
Try changing the cable box setting, and the box may also have an auto feature. But you'll want it to be on widescreen. Here's an example of the option in a cable/sat box:
Set your TV in a 16x9 setting, and then adjust the cable box. From there, see if the options work better for you. If not, it may be necessary to manually switch.
Keep me posted.
I just set up my Samsung PN50B550 last night and was a little freaked out at first. Many of the channels (both SD and HD)had this strange pixalation problem like you would see if you had satellite TV and there was a big rain storm (I have cable). Anyway, once I switched the HDMI cable out it seemed to get better and I think that problem is gone.
I was a little disappointed with the picture. I think the choices I have are bright, movie and standard (or something like that). I know the settings can be adjusted but was wondering if I am supposed to wait a while to do that?
Finally, I know I am doing something wrong with the picture size. The non-HD channels are showing up with the black bars on either size. I know the reason for that and I know I can push the button on the TV remote to change the picture size, but what a pain. Is there any way to change one of the settings so that the picture automatically fits to fill the screen for non-HD but knows to go back to the regular setting for the HD channels? I hope that makes sense.
If anyone has any other tips for a Samsung newbie who wants to get the most out of their TV I would really appreciate them!