These lectures are also available on iTunes U. It would be interesting to compare the number of YouTube views to the number of iTunes downloads. I watched the first two classes on YouTube, and downloaded the rest on iTunes, though admittedly I'm still only on lecture 6.
here is the number of views for Andrew Ng's Intro to machine learning course on youtube (http://www.youtube.com/watch?v=UzxYlbK2c7E )
lec 1, 206612
lec 2, 91234
lec 3, 49000
lec 4, 36823
lec 5, 27782
lec 6, 26347
lec 7, 22075
lec 8, 20713
lec 9, 15665
lec 10, 14142
lec 11, 16573
lec 12, 14296
lec 13, 12401
lec 14, 15022
lec 15, 12290
lec 16, 10760
lec 17, 8986
lec 18, 13639
lec 19, 10219
lec 20, 11373