What are you up to?

Dion laments the lack of a good calendar solution:

We have great calendar clients such as GCal, iCal, 30boxes, etc etc, and we have simple standards such as ics, and hcal but I still have a nightmare with calendars.

I've heard a lot of enterprises feeling this pain as well. Most of 'em have standardized on outlook, which is pretty limited in terms of supporting multiple calendars. A couple of use cases I would like to see supported:

• Let me see a calendar showing milestones in the projects I'm interested in (and no, I don't want to create and manage a seperate calendar in Exchange - I want Exchange to be able to read and write using a standard format that is also supported by my enterprise project portfolio planning software).
• Let me pull certain types of events from individual calendars to create a read only unified view (e.g. vacations) across a group.

Security, via an ACL, would be key.