From a Techcrunch entry about online television networks that guesses why Al Gore’s CurrentTV has yet to take off:

It’s not hard to get your friends to watch a horny donkey video, but try getting the same group to watch a video on teaching abstinence in schools.

I would add that the licensing scheme is (or was when the site first launched) not all that appealing, in that Current owns your content once you post it there. There’s also the factor of automatically shutting out half the audience by having Al Gore as frontman.