This subject has been done to death over and over again. OK, I do watch the Safety Briefing as a courtesy to the crew, but in actual fact I have already briefed myself before the demo has even begun. That's because if the $hite hits the fan I want to be prepared and I have a plan (well more than one, depending on the circumstances).
Reading comments on forums from crews advocating the wisdom and courtesy of paying attention to Safety Briefings, I am remimded the fact that one of the flights I regularly travel on always includes a positioning crew (in uniform) on board. On all occasions I have observed how they have continued to chat and joke with each other as the demo is given! What a great example to the rest of the pax that is!