Besides security and caching, I think standards/interoperability are key. I want my next-generation apps to work on a cloud filesystem of my choice, be it Drop

Besides security and caching, I think standards/interoperability are key. I want my next-generation apps to work on a cloud filesystem of my choice, be it Dropbox, Google Drive, etc. That will be the most significant step towards a real cloud OS, and I bet someone's already working on it.