I kinda noticed "grainyness" with the display when viewing videos. Really didn't like it at all, and it looked bad compared to the Xperia S I had been using a week prior.
Well, I found that while the X-Reality setting made colours "pop" in videos and pictures, things seemed to get kinda grainy looking. I've been running with it off for a few days now, and I reckon it looks much clearer now. Plus, vids and pics don't look like they have been artificially tweaked with.