One of the projects that we’ve assiduously avoided doing is a shared calendar system for the whole University, on the grounds that there aren’t any plausible open standards and implementations, and we fear lurking scalability problems in the human side of things.
The iCal/vCal standard is fairly mature, but the associated Calendar Access Protocol is mired in committee bikeshedding (it’s on revision 14). In the mean time people like Apple and Mozilla are using WebDAV as the publication and sharing mechanism; there’s also an internet draft on this topic.
Perhaps this provides a plausible way forward for us, if the interoperability comes together…
(The small matter of a directory rears its ugly head too.)