Yup, I appear to be out of luck on the Christmas card thing. From a reader:

It is too late.
Sending them out now has the following effect:
1. If you already received a card from the person, it looks like you sent cards to everyone but them, because they were unimportant, and that you grudgingly sent them a card only because they sent you one.
2. If you did not receive a card from the person, you cause them to feel like a schmuck because they know it’s now too late to send you one and you defeat the whole “happy” experience of sending out cards as a way to renew ties with those to whom you don’t communicate with during the rest of the year.