Ubuntu One is a cloud storage service available on many platforms including mobile devices. With it, you can store your pictures, videos, documents and other files on a remote server that would allow you to access them from anywhere. It comes with 5GB of free storage: while this might be enough for documents, you obviously won't be able to fit many large files (but you can pay to get more storage space if you need it).
The interface looks great and it is well-designed. Indeed, the every element is rounded and there are tabs granting you fast access to different functionalities of this program: access folders, share links, add or remove devices, change your settings, and check your account information.
Many users are concerned about their privacy when using cloud storage services. Ubuntu One is an open-source program created by the well-established company, Canonical, that values users' privacy. In the privacy agreement of this piece of software, it is clearly stated how one's data is/will be used: 'We don't share your personal information with anyone except to provide you with services, products, to comply with the law, or to protect our rights'.
To sum up, I think that Ubuntu One is a good cloud service that will fulfill most of your needs for free. However, if you need to store large files, you will have to buy some extra space.