A local "mini-DAV" server for calendaring would be great, especially
if it could advertise via Rendezvous. That could make Sunbird (and
likely iCal, if it worked with the server, as well) a "killer app" --
instead of using Exchange or another big centralized scheduling
system, just let everyone maintain their own calendar, and locate
other peoples' on demand with mDNS.

Of course, there would be disadvantages -- namely, as you suggest,
that individual machines may not be running 24/7, which means that the
calendar data they publish would be unavailable. I suppose that the
local client (or WebDAV server, if it functioned as a proxy) could
cache the latest calendar, though.

-- 
Lennon
rcoder.net