As noted in the comments on the article below, there is a problem that affects some users that arose when the new contact code was deployed last night. We're still investigating but it appears that users who set up their contact sync some time ago were assigned authentication tokens that do not work with the new Google contacts API. The problem is fixed by logging into our web site and re-requesting access to your Google contacts data. This results in a new token being assigned.
This problem does not affect all users, we suspect only those who signed up several months ago. The real problem here is that our web site does not yet detect and diagnose the problem, and the 'green light' checker says that everything is ok. We will be fixing that later today once we figure out exactly how to detect the problem.
At present, if you had working contact sync yesterday, and now it's not working, and you see 'contact support' in the sync status page, and your account was setup a while ago, then please perform the request access procedure again.
Update: the web site now does detect and display this problem.