If you are then this article by our friends at theVerge will interest you. The Cloud is not full proof as many believe; some of the Cloud have been hacked and some of the solutions used have bugs as evident from this article. Check out "Storing Your Data on the Cloud?".
Theoretically, you should always maintain 3 copies of your data: backup located outside of you home or business, backed up to an external device and what you have stored online.