In addition to lectures we may want to include office hours, course outline for each lecture, a suggested progress plan/time-line created by the course developer/instructor and of course assignments. This may appear to overlap too much with a course management web application like WebCT and Blackboard (for example) but scheduling is the shared component.
The beauty of it is you can make as many cal's as you want, or shared resources...endless possibilities.
-- Can a calendar be shared with all or certain people/groups?
All those are possible! Many ways to share and give others permissions to edit your events-with notices going out to let people know you shared something.
-- Are there methods for importing calendars? If I were a student again I would like to be able to have the registrar send me my schedule as a calendar. I can then just import it to the application. Perhaps there is another way for sharing calendars?
There currently are several methods for importing and subscribing to calendars, just see the REST features below, but more options via the web interface for importing/exporting are coming shortly.
-- Can I subscribe to a calender like I do with RSS feeds and podcasts in itunes? This will allow me to subscribe to a department, university, course or seminar calender and automatically have it updated. The option to select which calendar viewed is already available.
When used with a calendar folder, the Atom feed will (by default) generate a feed of all appointments -/+ 7 days from the current time. To specify a different time range, you can use the start/end query parameters:
Search for 'REST'-to get you started:
http://www.zimbra.com/blog/archives/...st_update.html
http://www.zimbra.com/blog/archives/...st_and_no.html
I noticed that google calender allows for a single click to add an advertised event to my google calender. This is also a nice feature.
If the zimlet is turned on...Right click dates in your browser...it even shows you schedule conflicts!
Sound's like you need to try out the hosted demo: 
http://www.zimbra.com/products/hosted_demo.php