My MacBook Air (2012) is completely silent most of time (except viewing videos in Flash or Silverlight). Given is silent, I can actually hear the power supply of my monitor buzzing! (actually it's very quiet buzzing) - be careful what you wish for I guess.
Yeah I know it's awful, if my Celeron 450Mhz could play DVDs at no effort, I don't know why this can't play videos on 5-10% CPU and not spin up the fan.