web applications

While all this talk of Web x.0 and applications (such as word processors, etc.) running inside of browsers is going on, I can't help but feel there is one question left unanswered. And that is: Why do we want to run all of our software in this manner? Even Microsoft is starting to lean in this direction with their "Live" services. When will this end? I certainly feel more comfortable with all of my software and files on my local machine, but maybe I'm just paranoid. So what do people think about running applications or, even more ambitiously, whole operating systems across the Internet?

>>1
Why? Because we do not want stuff on our local machine. We want it in a safe place that can be accessed from anywhere in the world.