This particular set can have a problem with slight 'bowing' of the horizontal lines on the screen, basically a geometry issue. Over on AVS Forum there's an owner's thread for the HLTXX76 sets, and some people there attribute this to the ultraslim cabinet lacking rigidity. I just purchased the HLT5676 from Amazon, and what I see is that with a 2:35 film the black bars on the top & bottom are higher on either end by about 1/4" compared to the middle. I haven't really been able to watch more than a few minutes on the set due to remodeling going on in the basement, but it didn't seem to affect the picture. Some people on AVS say their sets don't have the problem at all, others have sent their sets back because of this and are damning Samsung for making the worst TVs in the history of the planet.
If I were you I'd go and take another look at the set in the store before you buy it and see if the problem is visible at all, and if you even care about it even if you do see it on one of the sets.
This review from May 07 is for the previous generation 1080P Samsung, but it's got some helpful tips about setting up the TV as far as menu options, etc.
http://ultimateavmag.com/rearprojectiontvs/507sam5688/
