Well there are many cloud storage services but most of them require you to upload your files for backup. They overlook the fact that we are so undisciplined that we forget to upload and repent when we need a file during a crucial time. That's where Bitcasa comes for rescue. Earlier I used SugarSync which worked great but they planned to go premium ending the free usage and thus I have to move to other service. And guess what Bitcasa works just fine for my backup needs. Just install this service on your PC and mirror any folder you need to backup. Like I work on many files and I save it on my desktop. I have just mirrored Desktop to Bitcasa and now I don't have to worry. I work on a file and save it, Bitcasa quietly takes the backup and stores the files on cloud. I can access these files from anywhere on any pc using their website or on my smartphone using android application. Its so cool and I strongly recommend this a try.
Below is the link to get your free Bitcasa Account.