Well, I'll admit I rarely will watch an entire safety briefing because:
I've already stowed my hand luggage in the overhead, or under the seat in front,
My tray is stowed,
I've put on my seat belt, which will remain on for the duration (potty breaks excluded)
I've already identified the emergency exits and the ones closest to me, I've counted the rows in both directions,
I've identified where the 02 masks will fall from,
I've looked at the safety card,
I've put my phone and iPad into flight mode and I'm prepared to put iPad to sleep. (Did anyone note that in both videos posted here that devices were not turned off completely!)
I don't ignore the briefing completely, for example I'll look up for the life jacket to familiarize myself with the ties/fittings. I find that much of the demonstration is telling you to do things that you've already done. To me it seems silly to be told to put your carry-on up or down, when you're already taxying and everyone has done it and the bin doors are closed.
But I'm not saying that other, less experienced, flyers should ignore the briefing.