Ok, I said I'd come back with a more positive view of calendaring. Here it goes:

The Calendaring and Scheduling Consortium
- "The consortium is focused on the interoperable
exchange of calendaring and scheduling information between dissimilar
programs,
platforms, and technologies." Now *that's* what I'm talkin bout. But
like any one of these interoperability groups, we'll have to wait and
see if it has legs.

The Open Source Application Foundation - Led by Mitch Kapor, this group is working on a PIM client that has sharing/syncing built into it's core.

iSync in OS X Tiger
- Supposedly iSync in Tiger has an extensible architecture that allows
developers to easily hook into it. Wow, that would be cool if it is
*actually* open, and doesn't just allow developers to easily hook into
.Mac...

Link