I have been using the client library to add CardDAV suppport to ASynK - a bidirectional sync tool that now works with Google Contacts, MS Outlook, Emacs BBDB, and now CardDAV. You can find more about asynk at
http://karra-asynk.appspot.com/
I would like to submit some of my patches back to the mainline. What would be the best way to do that? The most important addition I have made is the implementation of a MulitGet for CardDAV.
-Karra