[0]https://developers.google.com/google-apps/calendar/caldav
[1]https://developers.google.com/google-apps/calendar/
[2]http://caldav.calconnect.org/implementations/servers.html
To be honest though, there doesn't really seem to be much effort to even try - maybe someone famous will step forward and get the ball rolling?
I couldn't figure out a way to list all contact lists. You had to know the name of the list and use it in the URL. Even at that, you can only access contacts in "My Contacts" or other groups. There's (seemingly) no way to access "All Contacts".
CardDAV is 'supported,' but not very well. It's definitely a second-class citizen.
Google has an API now, but who knows if it'll be there tomorrow. Google does not have a great track record at this point.