2 new and VERY cool projects that use content on You Tube.
The first is called the ThruYOU project which mixes unrelated youtube clips to make some amazing tracks.
The second, is Muziic. A 15-year-old has created a free-music service
by harnessing YouTube's vast library of music videos. Muziic, created
by teen developer David Nelson, has built an iTunes-like interface on
top of YouTube. The service enables users to stream YouTube's music to
their PCs without fiddling with videos. Users can build playlists and
organize songs in a way similar to iTunes. Click on the pic below to view in a larger pop-up.

I downloaded the player and it is SLICK. I wonder how long until YT shuts him down...
The CNET article from March 8, 2009 with the details