I have used YouTube legitimately in 3 of my 5 classes this term. Some excerpts of awesomeness:
21M.423, Conducting and Score Reading. We actually had an essay where we were required to watch conductors in rehearsal and comment on them. This generated some humor-filled finds:
Bernstein conducting Overture to Candide: (:30 and 2:30 are the best parts!)
http://www.youtube.com/watch?v=422-yb8TXj8 And the conductor isn't exciting, but watch :46 seconds in:
http://www.youtube.com/watch?v=lEg-Y5llBnI And from 16.400, my human factors engineering class:
Guy getting sucked into a jet engine (don't worry! he lives!):
http://www.youtube.com/watch?v=L_gpPbpONK4 Bad case of pilot induced oscillations in the F-22 prototype:
http://www.youtube.com/watch?v=Ieef0tLrv9c TGIF!