Good news:
The extensions used in the Calendar feed will definitely be documented and those docs should be available soon. The Calendar Data API support (these feeds plus the ability to programmatically create, query, edit, and delete Calendar events) isn’t officially launched yet… the release is going to be slightly staggered from the main Calendar Web UI launch that happened today.
[More here]
[Update] The API is now (4/20/06) out.
Related posts:
It’s just in time for their enterprise push – OM has little write up here: http://gigaom.com/2006/04/18/google-finally-has-an-enterprise-plan/