Ooh, ooh!
I just bought the aforementioned Samsung PN51D550 last night, $999 at Best Buy, and I love it!
Burn in, I can't answer for. Regarding 1080p 600Hz (yes six hundred!) I can answer! Absolutely no (as in zero, nada, zilch, nothing) motion artifacts!!!! No pixel storms as the camera pans to follow a golf shot down the fairway.
Can't answer about 3D, either, doesn't come with glasses, they are sold separately. Personally not real interested in 3D. Everyone who's tried it in GT5 has come back with "So?" and movie demos I've seen have been the same . . . "So?" Avatar was especially bad. A series of flat spaces one in front of the other: flat background, flat place for other background items that are closer, flat characters a little closer, slightly shaped characters still closer.
So who cares about 3D? It ain't there, yet.
OTOH, Portal 2 on PS3 was gorgeous, even though 3D is not even an option with it.