I signed up for Canonical's UbuntuOne private beta last week and just got my invite today. The service lets you upload files to Canonical's servers where you can seamlessly sync directories and files across any number of computers. This is generally known as 'cloud storage.'
When you sign up, you are directed to add their UbuntuOne repository and download/install a small gtk applet (only compatible with Jaunty and higher) that will integrate the service with your Ubuntu installation. On my Karmic alpha system, the applet had already been installed, which is what led me to seek out the service in the first place.
There are two main ways to access your cloud data: via the aforementioned system integration or through a fancy AJAXy Web interface:
The Web interface gives you a lot of management options, including file and folder management:
as well as options to add more users to share your files:
The GNOME integration is also super-swanky, with a notification bar applet that lets you connect/disconnect to the cloud:
and a folder that appears in Nautilus with a handy button that handles connecting:
I haven't run into any bugs/issues yet, but I'll update this post as things arise.