async: There were discussions some time ago on the ietf-calendar list about XML iCalendar. I think it died on the vine, and honestly, I think that's a good thing. At any rate, RFC2445 is still being revised and updated on the IETF standards track, so if you disagree with something about how it does things, speak up on ietf-calendar. Standards are good, and the standard is leaning away from XML. There's no reason to reinvent your own wheel, poorly.
Reefknot and libical are the two major calendaring projects/libraries I know of that parse and use iCalendar. (libical is the core of Evolution's calendaring functionality.) Mail me if you want more detailed explanation or if you'd like to get involved with Reefknot.
You might want to check out the Reefknot Bootstrap Guide (an intro to iCalendar) or the Reefknot Developer Roadmap, which is slightly out of date but is still essentially right. The Reefknot website has other links you might find useful as you start to learn more about iCalendar.
Nothing much going hackingwise--- saw *Traffic* last night. Getting my bike fixed up to ride again; determined that the Broadway Bicycle School is indeed very cool. But I knew that already.