What are the needs for WebOSes ?

I was just playing with YouOS and wondering what are the needs for such an OS (if we can call this an OS, this is another debate).

1/ One first property is that it can be accessed from any web-2.0-capable device in the same manner: from the office, at home, from a mobile device.

2/ Another important thing is that people don't need complex operating systems any more for simple operations: listening to music, watching videos, browsing the web, chatting (see my previous article on linutops).

WebOSes might be the future of desktop computing. Anyway we have to mention that people won't like their datas to be stored in a remote server: passwords, bank account numbers, illicit mp3's, etc, so we have to find a solution for this.