I am not sure how long this functionality has been available from YouTube but I recently noticed a small tab underneath the video showing a link to download the music from the video via iTunes. Now while I would probably not buy the music from iTunes (although they have rethought their DRM policy) it does provide the opportunity to learn track details and provide similar.

iTunes in YouTube

Partnerships like this will are what makes the internet continue to evolve and change and I look forward to seeing more convergence like this.