Youtube is rolling out video downloads for some selected partners:

YouTube
is trying to find more ways to monetize the popular web service, and recently started a test project with selected partners who were invited to start offering video downloads to interested viewers. Now it seems the Google-owned online video community site is ready to expand the program to other interested partners based in the U.S.
As we noted earlier when we first caught wind of the download service, selected YouTube partners can offer their video downloads for free or for a fee (determined by the partner), paid through Google Checkout. Most videos in the test charge about $1 each. The partner can also decide how the downloadable video will be licensed to the user - whether it will be restricted to a private non-commercial use video, or whether it can be used under Creative Commons.
It’s not entirely clear if Google / YouTube is currently taking a cut on the for-fee downloads during the test period, but it will most likely do that at some point if it isn’t already.