I ran into the video on a non-usa mtb site. They used it to advertize the SRAM X.5 derailleur being better over the Shimano Deodore one. (their claim of course) They were trying to sell SRAM components. Is hard to tell from the video to see if the used the same trail, speed, gear, rider weight and any other factor that comes into play with chain slap. But from just watching the video, you can see that the SRAM x.5 derailleur seats a bit more paralell to the bike's rear chainstay then Shimano. Based on the red and blue lines they showed over the video, they were trying to prove that the Shimano derailleur was moving up and down more and causing more chain slap then the SRAM.
Make your own judgement, I don't claim preference on SRAM over Shimano. I've only had one read MTB bike and did go from Shimano deodore drive train to SRAM X.9/x990 cassette. Someone was selling theirs and I was at the right place to get them. I've never given XT or XTR a try but I am sure I would be as happy with them. XT is ligther or just as light as X9 and XTR vs X0 are very similar too.
Anyways, just never seen the derailleurs in action as I saw them on this video. I thought it would be some intestest to some of you to see it too. I don't mean to start a WAR between the two. :-)