Marc Andreesen once said that "the combination of Java and a Netscape browser would relegate the operating system to its original role as an unimportant collection of slightly buggy device drivers." Pretty funny, considering Microsoft has fifty billion in cash and Java is nowhere to be seen on the desktop.
In fact one could make a thin client platform out of one of these AJAX technologies and then replace the OS with a minimal set of services, like the GEOS operating system. Feasible but highly improbable, at least on the desktop. Yet if some new device appeared, larger than a cell phone but smaller than a laptop, it's a whole new ball game. Instant-on is a feature I would dearly love to have, and it's not going to happen on Windows.