Hi, I just bought a Samsung LN52B630 and it seems to be having the same sorta problem. Also if I put it in "Game" mode it will turn off, turn back on, and go back to a different setting ("Dynamic").
I think I read somewhere that Samsungs are known to have some issues with the capacitors so I would think that would be the first place to look. I'd give Samsung a call though cuz you and I paid good money for these things and deserve to be able to enjoy our products!
My tv just started to turn itself off and then turns on and is starting to happen more frequesntly. Its as if someone is sitting on the On/Off button on the remote. I have tried to track this to see if there is a pattern but haven't found anything yet. Nothing is hooked up to it other than the cable box which has had no effect from what I can tell...disconnected the cable from the box and ran directly into the TV. Tried that and still shutting off and then on by itself.