As a provider of secure cloud storage (vitalesafe.com), I can tell you that this is anything but easy. It appears easy on the surface, but collisions (files changing on multiple clients simultaneously and files changing while they are being uploaded), locking, versioning, etc. make this much more difficult than it first appears. Add in the cross-platform (Mac, Windows, Android, Symbian, iPhone/iPad) requirements as well as multi-lingual character sets and differing rules about folder/file name rules and this gets to be quite complex. I've had more than one user (and even IT professionals) say all they want is a "simple online storage solution" but don't understand the ramifications of limited Internet upload bandwidth. If you add a secure requirement, which introduces complexity that end-users HATE, and this is no small task. What users seem to want it 100% security, 100% bi-directional synchronization without any user intervention, and 0% additional complexity.