Is this for your personal system, or business? How reliable is the backup itself(run random tests periodically). What are the issues with handing possibly personal information to a 3rd party? What happens when you lose internet connectivity and need to restore a file now? How long does it take to complete a back-up over your internet connection? Are you keeping old backups(archived), or is there really only 1 backup(can you get a version of a file from 6 months ago)? There are other things to think about I'm sure.
I think you have to come to the realisation that putting data online (in the cloud) has the potential to opening that data up to an unkown set of eyes. There isn't any way to confirm who does and does not have access to it.
Even for personal use I encrypt online backup data and for businesses I would be reticient to put any financial and client data in the cloud. In fact PCI-DSS makes it almost impossible to put credit card data into a cloud environment.