Great Job All! How about a client for Windows Phones since a client is working for Windows 7? Keep up the great work.
The Ubuntu One client for Windows doesn't really bring us much closer to a client for the Windows Phone platform. Our desktop client is written in Python (and shares most of its code with the Ubuntu version), while WP7 apps need to be written with XNA or Silverlight.
Also, the desktop client works in terms of synchronising all of your files locally, while on a mobile platform where storage is limited and bandwidth constrained, it is more useful to be able to browse all of your files and only download the ones you're interested in (which is how the Android files app works).
While we don't have immediate plans to release a WP7 native application, the API that the Android client uses to access the service is publicly documented if you're interested in developing an application yourself:
You also have the option to use Ubuntu One's web interface to access your files.
You could try out this app, although it seems to only implement the filestorage API.