Wow, another episode on 'sometimes computers can be really difficult'. What i wanted to do, was to sync my address book on my MacBook Pro, running OSX 10.7.2 Lion) with my Google Contacts.
Of course, when you Google on how to do that, you find lots of info, and it seems very simple :-). But, for me (and i found for many more), i ran into problems.
When i proceeded like described as how it should work, i would be able to enter my Google login credentials, and see "connecting to google". But after that: nothing would happen.
Digging around, i concluded i needed to see what was going on under the hood. Now this is something to remember if you run into things not working: on OSX start Console (note: NOT terminal). You can use Spotlight to find Console. Console shows you any errors occuring. Now don't panic when you see messages you don't understand. Just let your eyes go over the log text, and see whether you see anything that might give you a hint.
In my case, whenever i started a Sync from within Address Book on OSX, the errors "Address Book: failed to save to keychain" and "Address Book: failed to retrieve from keychain" would pop up. So apparently, something was wrong in that area. Whether it was the blocking problem, was unclear, as you sometimes get error messages which don't stop you from eventually getting what you want.
I opened Keychain Access, which you can also find through Spotlight. I first deleted the Google- and Gmail-entries i found.
But that did not solve the problem. I also tried to Verify (found no problems) Keychain (under the Keychain main menu, Keychain First Aid), but: no progress. I decided to choose "Reset my Default Keychain" under the Preferences. And tried another sync from within Address Book. This time, i got an error about Keychain! It gave me an option to revert to default (or something, i did not jot down that message). I thought: what the heck, did it, and it sync-ed!
I hope this helps. Seems Keychain can somehow block a proper sync. There may be a more elegant way, so if anyone finds it, please leave a reply!