[Brian]

Dirk, CalDAV is a feature that's only present in Mac OS 10.5 and later; since OmniFocus 1.x releases need to support users on Mac OS 10.4, CalDAV isn't supported.

It is under consideration for inclusion in a future version of OmniFocus; if you'd like to see this added, use "Send Feedback" under the Help menu to let the support ninjas know. They'll add your request to our development database.