, AndyC wrote

No sign of that here, but I haven't used Outlook 2010, only WLM and Hotmail/GMail directly. Have you ever used anything else to access your mail/contacts? I'm wondering if something else possibly inserted some faulty birthday info at some point?

I can't think of any.  It's strange, though.  I've double checked some of my contacts information in Outlook 2010 and Windows Live Mail, and they're fine.  I don't know about Facebook, though.  Perhaps this info came through their contact information.  I'll take a few and check....

.... OK, I've just checked.  Of all of my contacts that I got a notice of as having a birthday on January 1, only 4 of them are friends of mine on Facebook.  All of them have specified their date of birth, and none of them are January 1.  So, it didn't come from Facebook, either.