The Mac client of Ubunto One does not work for me, so I'm using only the web interface. What bothers me a lot is the lack of a few essential features of the web interface:
Theres is no sorting option as long as I've looked around. It would be great to be able to sort files by name, upload/modification or creation date. This is a standard feature of most web interfaces for e-mail, for example.
Downloading and uploading files can be done only on individual items. Having the ability to select a few items and download them as a "zip" archive would simplify the things tremendously. Once again, multiple selection for some common action (like deleting) is something most email web interfaces allow users to do. It is frustrating not having such option in Ubuntu One.
Moving around files should be made easier - by the same multiple selection mechanism that would allow one to copy or move files to a given folder.
If any of these features is already there but I could not find it, I would be glad if you could tell me. If there are plans for such features, that would be great to. If you think I should file a bug report for a "wishlist", please let me know.