We're getting very, very close with CalDAV. Draft version 09 is submitted and I'm sure it will be posted soon. There's not a lot of open issues remaining (one is how to use ETags, which is the topic of lively discussions in both the CalDAV and the WebDAV mailing lists). Interoperability is pretty good already -- I got a great reception at ApacheCon when I demo'ed Chandler publishing a new event to a calendar shared on Cosmo, and then used Sunbird to refresh the shared calendar and see the new event (note that Chandler 0.6 was just released so you can do this too). We'll have one more interoperability event in January before likely finishing the draft and submitting it. We plan to do pseudo-last-calls in WebDAV and CALSIFY WGs but if you've been waiting to read the draft, it's great to get comments even before last-calls.