Nick, you might be interested in this quick thing I just wrote up:
http://arsdnet.net/articles/web-apps.html
A few years ago, I was talking about a new windowing system...
and believe it or not, I'm still slowly moving forward with it,
but I think existing X is good enough to start with for this idea.
My old thing was about thin clients used through the web. Well, I
like downloading programs too sometimes, can we solve that
problem? Web apps do an ok job, so do app stores. Let's get the
best of both worlds: download a program that targets a standard
Linux VM distributed with browsers. I go into a bit more detail
in the link.