Portable functionality on limited systems, where the limitation is not technical, but policy-based (i.e. display systems that you can't break out of the web-browser on.) Not the most righteous cause, but a cause nonetheless.
Every couple of months one of these wanders along by. They are looking slicker these days but they all have the same problem:
They are just OS mock-ups that don't do anything running in a browser.
When I can upload a vmware image and then run it quickly in a browser from anywhere, then we might have something, but until then, toy versions of real apps running in fake desktops are cool, very technical, and very impressive, but not useful.
I can almost feel the vibe of something like this coming from amazon EC2 eventually. Something with EC2, nomachine, persistent storage, vnc... its almost all there. Sounds like a ycombinator startup to me.