This works exceptionally well on viral vids that are share worthy or when you offering free information. The video that is being shared around can then lead back to your fan page or website (if you set it up correctly to do this) even if the video is not originally yours. It's a brilliant strategy that is becoming more widely used due to it's success rate.
I can add this share feature to any youtube video you wish to share or any that you have created and self host.
Check out my other gigs for further facebook video marketing assistance.