There are so many Did You Know video's that I thought to share the motherload.
This many versions available speaks to the copyright vs. copyleft issues of mashups.
They been around for two years in various versions, courtesy of Karl Fisch, Scott McLeod and Jeff Brenman.

To learn about the issues mentioned above read
Dr. Mashup; or, Why Educators Should Learn to Stop Worrying and Love the Remix