The soundtrack was an enormous success. The song "Magic" went to #1 on the US pop singles chart. In the UK the soundtrack album peaked at #2, and the single "Xanadu" was #1 for two weeks in July 1980.
According to the special features on a recently released DVD, the cartoon sequence was added because the filmmakers needed to include an extra song written for the movie. Having a cartoon made for the song was easier than trying to make it fit into the movie.
The choreography in the Gene Kelly-choreographed "Whenever You're Away From Me" is nearly identical to the choreography in the title number from For Me and My Gal (1942), in which Kelly starred with Judy Garland.