Canonical introduced Ubuntu One in 2009 with the release of Ubuntu 9.10. The service offered 5GBs of storage. If you opted for the paid Ubuntu One Music service for $3.99 a month, you also got music streaming and additional 20GBs of storage.
If you follow personal cloud storage at all, you can already see the problem Canonical was running into: They weren't offering enough storage at a low enough price.
As Jane Silber, Canonical's CEO wrote in the company blog, "The free storage wars aren’t a sustainable place for us to be, particularly with other services now regularly offering 25GB-50GB free storage. If we offer a service, we want it to compete on a global scale, and for Ubuntu One to continue to do that would require more investment than we are willing to make. We choose instead to invest in making the absolute best, open platform and to highlight the best of our partners’ services and content."
So, as of April 2, 2014, "It will no longer be possible to purchase storage or music from the Ubuntu One store. The Ubuntu One file services will not be included in the upcoming Ubuntu 14.04 LTS release, and the Ubuntu One apps in older versions of Ubuntu (and in the Ubuntu, Google, and Apple stores) will be updated appropriately. The current services will be unavailable after 1 June 2014; user content will remain available for download until 31 July, at which time it will be deleted."
Silber promises that "We will work to ensure that customers have an easy path to download all their content from Ubuntu One to migrate to other personal cloud services."