Safari 3/Leopard does not support RFC4709
Even though the IETF approved RFC4709 back in November 2006 - and Leopard has a far improved WebDAV implementation compared to Tiger (well, it beachballs less anyway) - the simple proposition of 4709, the addition of a MIME type to handle automatic WebDAV mounting to the desktop via Content-Type: application/davmount+xml hasn’t yet been implemented.
Pity. I’d been kind of hoping it got in. Hadn’t gotten around to checking it but just assumed it would work - it doesn’t. Maybe in 10.5.2? 
UPDATE: It’s included in /private/etc/apache2/mime.types, so at least the bundled server implements the RFC …
UPDATE2: I want to implement this to enable ultra-simple asynchronous filesharing between me and my friends.