As an industry, we have simply not designed our calendaring and directory software and services for this “mesh” model. The websites, services and servers we build seem to all want to be the “owner” and “publisher”; it’s really inconsistent with the model that made email so successful, and the loosely-coupled nature of the web.
Ray Ozzie (creator of Lotus Notes) proposes something called SSE (Simple Sharing Extensions) — an extension to RSS. Read on for more juice. §