I.e: a secretary saves files to their D: drive, and it's in the cloud. And when you run out of disk space, you buy more from your cloud provider and suddenly there's another 10TB on your D: drive.
I find this very neat as it brings cloud benefits (around reliability and expansion) to real people, using crappy early 2000s desktop apps - ie, most people using computers.
Jesse's blog port on the launch: http://jessenoller.com/2010/02/09/say-hello-nasuni-launches-...