Shared contacts, the cheap & cheerful way

I’ve been meaning to write more about groupware and collaboration, and hopefully will find the time for a longer post on the topic, but here’s a bit of timely news. Ludovic Marcotte and friends have just released a combination of some of their previous extensions to Thunderbird and Lightning as something they call the SOGo connector: it’s an extension to Thunderbird which, when combined with Lightning, provides features like remote address book through CardDAV (sending vCards through CalDAV, AFAICT), and an informal protocol called GroupDAV. While CardDAV is an extension to CalDAV which is an IETF spec, GroupDAV is currently an ad-hoc, simple protocol built to let clients interoperate with open source groupware servers, which probably explains both why it’s simple and why only a few servers (including SOGo, of course) support it.
I still need some education as to what relevant standards have to say (even in non-final form) about shared contact lists. More on this topic later I’m sure.