Here's a hypothetical scenario that is _almost_ possible right now...
# Boot up your PC with some tailored Linux derivative.
# You're presented with FireFox in full screen mode without toolbar, tabs, etc (note: no Linux login screen).
# You're prompted for a user/pass.
# You enter your user/pass and are authenticated against an OpenID server.
# An AJAX desktop now appears in front of you with "widgets" like sticky notes, weather, news, plus various icons including "Photo Album", "Search", "Writely"
# Clicking on "Photo Album" opens up "Flickr":http://flickr.com in a "window" on your AJAX desktop.
# Clicking on "Writely" opens up "Writely":http://writely.com in another window on your desktop so you can create a document.
To me, this is a really exciting possibility. This type of scenario leads us back in to a client/server style system _except_ that the time shared mainframe is now the Internet!
There's a few hurdles though:
* How do local devices interact with web sites? E.g. How would you upload a picture from your camera to Flickr?
* Web multimedia isn't quite there yet.
* Privacy of data.
* My understanding is that Javascript can not interact with your local system.
I'm sure there's many other issues. Still, I think there are uses for this type of technology right now (Internet cafe, libraries, mobile devices)? The issue is that the scenario described above lacks features, but it's fundementally sound. There's a few gaps to bridge but they aren't too large.