I'm rather late to this party , but around the time Google ended ActiveSync support for unpaid accounts  they added vCard 3 (1998) based CardDAV support . Up until then one could sync iOS and OS X mail and Calendars via IMAP and CalDAV, but Contact sync was only via Active Sync. 
As we all know, synchronization is hell. Even if Apple and Google actually used the same vCard spec (probably vCard 3, 1998), and even if they agreed on newline characters, they still have to deal with distinctions between their internal data models and vCard. Some of those data model gaps are non-computable. . Even thought Google and Apple have similar 'Group' models that relationship metadata is ignored .
That said, at least CardDAV is relatively Apple friendly. Most importantly, this standard means, for the very first time I know of , there's a somewhat supported way to synchronize Contacts between Google and OS X Contacts and iOS contacts.
I've begun using it on Mountain Lion. Since I use Google two factor authentication I had to use one of their totally-defeats-the-purpose-giant-security-hole-not-single-use-god-i-hate-passwords-humans-are-losing-the-battle alternative passwords. There was some kind of transient authentication glitch but on a second try it worked. After a few minutes I had all 634 of my Google "My Contacts" on my Mac. Because of the long history of my Google/Apple Contact sync efforts (See Also, below) these largely duplicate my Address Book/iCloud contacts -- but Mountain Lion Contacts.app seems to merge the duplicates when I search .
This looks promising in a terrifying sort of way. You can drag and drop contacts between the iCloud and Google Contact lists; they'll be copied.
So what about Snow Leopard? Many fine machines run Snowie (and should not upgrade to Lion even if they theoretically can). They're (more or less) cut off from iCloud. Does CardDAV sync work with Google now? I wonder about adopting Hsiaio's technique, but so far the answer is no (same with Yahoo CardDAV). I didn't find much research on this question, but I suspect it's a combination of 10.6 bugs and SSL requirements. . There is some limited Google Contacts sync on Snow Leopard that some still use.
- fn - lots
 Google grandfathered my half-dozen Google Apps accounts and recently extended the termination date for non-Apps users.
 Google says Google Apps accounts should use "Google Sync", which is their implementation of Microsoft's Exchange Server derived ActiveSync (with different bugs one assumes).
 vCard over HTTP/WebDAV. vCard has been Apple's Contact/Address Book export option for as long as I can recall, so it may be a good match to their Contact data model. CardDAV is also used by Apple's ancient Address Book Server. vCard 4 2011 has old-style and XML representations, but I suspect Apple, like Google, is more or less on 1998's vCard 3.
Google's vCard implementation has limits; worse the only partly implement the 1998 vCard 3 spec: "why did Google move the ADR extended address "Oak and Pine" into the street address component? And worse still, why did it separate the two using an '\r\n' (CRLF) sequence? The VCard 3.0 specification clearly states that CRLF must be escaped by the single escape sequence '\n', not by '\r\n'".
 Reading the last line of , by the way, a penny dropped. Apple changed the way they handled CRLF and vCard between MobileMe and iCloud, with near-disastrous consequences for my OS X Contacts. By Darwin, I hate the ancient DOS/unix/mac line newline debacle.
 Meaning data loss is inevitable, transferring a Contact between systems won't return the original. Incidentally, under my TrueName, I've spent 15 years dealing with interoperability issues in healthcare - from HL7 to TermInfo to SNOMED/RxNORM and back again via cCCD and the like. If you understand why CardDAV is hard, then you have a glimmer of a smidgen of a hint of an idea why we don't have true interoperability between EpicCare and Cerner -- and why we won't for decades.
I think the people who trudge away on vCardX are heroic figures who should be carried upon our shoulders. Forget Ive, these people do the work I rely on.
 The marketing/interest problem is unsolved -- largely because of the spam/advertising counter-current. I'm very interested in productivity software and I follow a number of related feeds; but I still miss news like this.
 Check out "See also" - lots of history here.
 Looking at Apple's braindead implementation of iOS Contacts and Groups I'd pin this failure on Cupertino and Apple's corporate silos.
 A friend of mine has a 10.6 MacBook and needs to use Google's world (as do we all). I think the easiest way to manager her Contract migration will be to get them to iOS/Google and then use Gmail web on Mac. I may put them on an account on my ML machine to help with cleanup.
 So which gets edited when one clicks "Edit" in Mac Contacts.app? Don't ask those questions. OS X doesn't say.
See also - via Gordon's Tech
Yeah, I've been fighting this war a long time. February 2009, almost exactly 4 years ago, was a big series of battles, but the 2008 PalmOS to iOS migration was probably the worst (later there were tools). I've read recently that Apple is an intensely siloed company -- that explains why iOS and OS X contract integration is so very bad.
- OS X 10.6: Synchronizing Address Book to Google Contacts 9/2010 - Snow Leopard sort of synchronized to Google Contacts, but Apple never finished the job.
- Migrating Contacts from Outlook/Exchange server to OS X Address Book via MobileMe: 8/2011. MobileMe was working well when Apple killed it.
- How I synchronize OS X Contacts with Google Contacts and my iPhone 1/2011: I was using Spanning Sync to connect Google Contacts to a set defined in an Address Book Group. I did that for about a year but I think it foundered on OS X and iOS updates. Eventually Spanning Sync gave up -- understandably. I still use and recommend their Contact Cleaner.
- Googaby: Novel approach to Google Contacts and OS X Address Book integration 2/2009: It's still sort-of-living, but I think Lion killed it (Lion was an impressive killer). I haven't tried it.
- OS X Address Book to Google Apps Contacs using Google ActiveSync 2/2009: It didn't quite work.
- iPhone sync to Google contacts - 3 methods and work/home implications 11/2008: Five years later we are still struggling with the same issues.
- Project Contacts: Integration across iPhone, Google and whatever 2/2009: Slow progress indeed. Contacts have been hard.
- Project Contacts: Now mixing Outlook/Exchange, PST file, Outlook/Home, MobileMe Sync, OS X Address Book and the iPhone. 5/2009. Shudder. More struggle.
- MobileMe: Integrating Work and Personal Contacts 5/2009: MobileMe was pretty good around mid-2009 and then continued to improve. iCloud still isn't up to that mark.
- iPhone Google Sync - Mail and Google Apps and Google saves my iPhone 2/2009: Did a lot that month! Google's original ActiveSync implementation saved the iPhone for me. I was ready to toss it out a window.
- Work home contact integration: Outlook to Google to OS X Address Book
- I try NuevaSync on my secondary iPhone 2/2009: They are still around. Alas, no OS X support.
- MobileMe to iCloud - Is Apple getting nervous? 5/2012: I keep reading how much better iCloud is than MobileMe. That's not my experience.
- iCloud transition went as expected - disastrously 6/2012: My Battle of the Bulge. Ugh.
- Consolidating Contacts: From Outlook to Address Book via MobileMe and the 5th Circle 9/2011: Migration from Outlook. Has to be a better way.
- Sync heck: CalDAV vs Exchange Server - a Google Apple review 2/2010: These days CalDAV might be ahead, but each has merits. I'm still on ActiveSync, but in 11/2009 I tried it the other way: Big switch on my iPhone sync: CalDAV and Exchange server.
- Plaxo - just not a good feeling 5/2009: Now we surrender everything at the drop of a hat. They are still around.
- MobileMe, Microsoft Outlook, Exchange, iTunes and yes, sync Hell 10/2008. I'm having flashbacks now.
- Palm to iPhone migration - address book and notes: 8/2008. Moving from Palm to iOS was exquisitely hard.