iCloud does only backup your iTunes music purchases.
"What is backed up
You get unlimited free storage for:
Purchased music, movies, TV shows, apps, and books
Notes: Backup of purchased music is not available in all countries. Backups of purchased movies and TV shows are U.S. only. Previous purchases may not be restored if they are no longer in the iTunes Store, App Store, or iBookstore.
See also: http://support.apple.com/kb/ht4859