YouTube is adding another source of revenue to its site: links to iTunes and Amazon. Recently, YouTube added banner ads to popular videos as a way to monetize the site. This form of advertisement should be much less intrusive than a banner ad. It will also make more sense.
Take a look at the top videos of all time. What do you notice? An overwhelming amount of them are music videos. Adding a link in the video to purchase the song will help drive sales. The Pandora Application has this feature built-in to it, which has cause me to spend at least $50 on various songs.
