As per the Ubuntu documentation, Ubuntu One now supports access behind a proxy:

https://one.ubuntu.com/help/faq/does-ubuntu-one-support-access-behind-proxy-servers-118/

“Proxy support is enabled in Ubuntu One on Ubuntu 12.04 and the 3.x version of the Windows client will have proxy support.”

With Dropbox having the jump on them for so long taking so much established market share, and with with the advent of Google Drive, will Ubuntu One have a chance in the cloud storage market?