I recently purchased the same model and am trying to decide whether it's worth taking it back and downgrading to 60Hz as well. Turning off Auto-Motion PLus hasn't really helped much (especially when playing high quality xVid media via the USB input). I've noticed inconsistent audio/video sync as well. I love a crispy sport-image as much as the next guy, but not at the expense of movie-watching (my main use for this screen).
Bought a Samsung LN40C630K1F because the 120Hz really looked much better in the store than the 60Hz Samsung in the same size/style. Between the comparable Sony and the Samsung, I judged it a tossup on appearance/features/cost and went with Samsung due to reputation.
Since setting it up, I have experienced extremely annoying issues with Soap Opera Effect (SOE) on both broadcast and DVD signals, judder on some broadcast stations, and audio/video sync primarily on DVD inputs (on both BD and std DVD). It is so bad that my 10 year old referred to an old CRT TV in the house as "the good TV". Part of that is likely that we're used to seeing something of lesser clarity so the clarity of this HD set is a bit offputting, but part of it is that the artifacts of the video presentation are quite distracting.
I have been able to overcome the worst of the SOE using some of the tips on forums on this site, but no luck so far with the audio/video sync. It doesn't occur 100% of the time, nor is it specific to standard DVD or BD. This alone may prompt the return of this specific set, but I'm trying to decide if I want to stay with this model/technology or not.
Any iron-clad solutions to either of these issues would be appreciated. However, what I would really love some feedback on is whether these kinds of setup issues are unique to the 120Hz technology. The last LCD TV I purchased was 3-4 years ago (so a 60Hz model), and it was pretty much viewable out of the box. If I were to simply go by the 60 Hz model, would I have to deal with all these setup issues? Is 120 Hz technology so new that all the kinks aren't yet worked out but may be in a year or two? It looks good in the store and all the technology sounds great on paper, but if I have to defect all the 120 Hz features to make it viewable, why not simplify life and just stay with the 60 Hz technology?