Matt Augustine (works in Ray Ozzie's Concept Development Team) presented a demo at the Supernova 2006 conference in the "Decentralizing Data" workshop, moderated by Tantek Celik.
The demo, available here as a screencast, shows how to leverage Live Clipboard + RSS Simple Sharing Extensions (RSS+SSE) + microformats (mRc?) to synchronize calendars in both directions between a web application (Upcoming.org) and a desktop application (Microsoft Outlook).
A new technique is shown, pushing client SSE feed state to the server via HTTP POST, to circumvent the difficulties of feed cross-subscription in firewalled environments. It also shows a tentative representation of SSE feed references in the Live Clipboard XML format.
More discussion over at Live Clipboard discussion list.
Here's the screencast
Microformats and hCalendar are a key piece of the demo. Talking of microformats, Yahoo! Local have added their support to their listings service. Niall Kennedy and Dan Farber have more on that.
Time to get microformats the t-shirt...