I'm not sure, honestly. We haven't had any reports of 'breaks' in Facebook today. However, Tuesdays are the day when they push out their 'big' changes. Sometimes, that does have knock-on effects and breaks some features on some sites.. it's pretty random.. and your site could have been affected.
I just tested on your site (wo*****nk.com) and was able to register a new account with Facebook. I then logged out and back in without any issue.
If you're still having the issue, can you let me know:
1) Is this happening for all accounts you try, or just a few?
2) Does the same issue happen if you use a different browser?
3) What about a different computer?
4) Have you heard this from your users, or just from your own testing?
We'll gladly do what we can to get to the bottom of it.. but from what I can see right now, things are working.. which makes it difficult to narrow things down.
Thanks,
Alex