As a dweller in the Apple ecosystem (or walled garden if you prefer) I enjoy a shared and automatically synced contacts list across my Macs, iPhone and iPad. Therefore I don't bother with Google contacts. Many people do, though, and for the Emacs users among them Julien Danjou has put together a nice Emacs extension that allows you to access your Google contacts from within Emacs. The package also integrates with Gnus so you can use it instead of the Big Brother Database.
Danjou says that it probably needs Emacs 24 because of its use of oauth2 but as I wrote on Monday and before, Emacs 24 is now in pretest and several readers have reported that it is very stable and solid. If you were looking for an excuse to jump into Emacs 24 and you use Google Contacts, this could be your opportunity.
Update Updated link.