Ubuntu One is not available for other Linux distributions. It also lacks certain 'basic' features found in competitors like Dropbox. One example could be the inability to sync the folder of your choice. On Ubuntu One you can only sync a folder within the Home directory. On the contrary Google Drive and Dropbox allow you to sync folder of your choice. Dropbox seems to be more pratical if you are a multi-booter as you can keep critical data on a partition which can be synced from all your operating systems. Ubuntu One can't do that.
So, here is a poll to understand which cloud service do you use on your Ubuntu OS. In addition we are also asking where you do keep your data- /Home or on the partition of your choice so that you can access it from Windows as well as Ubuntu.
You may also want to read if Ubuntu One has lost the personal cloud market.