As We May Hack "I can walk into any meeting anywhere in the world with a piece of paper in hand, and I can be sure that people will be able to read it, mark it up, pass it around, and file it away. I can't say the same for electronic documents. I can't annotate a Web page or use the same filing system for both my email and my Word documents, at least not in a way that is guaranteed to be interoperable with applications on my own machine and on others. Why not? - A Manifesto for Collaborative Tools
Yawp after me - "RDF! RDF!". But seriously, the answer to "why not?""
From Yawping!. The collaborative tools manifesto has been mentioned several times recently it's worth a look.