It will be interesting to see from where these cards are postmarked. That will provide a good clue about Google's seeming benevolence.

When I worked on medical records software, I looked into some companies that offered an API for sending snail mail. Doctor's offices spend a lot of time sending out form letters, and it seemed like it would be cool to automate sending out lab results letters. Obviously, email would be preferred (given patient consent), but physicians have to deal with the lowest common denominator (while blissfully ignoring illiteracy). Perhaps Google is experimenting with such a service? However, given all the things Google could provide to Apps users, this seems pretty low on the list.

I'd put money on this being an experiment or beta test in disguise as holiday cheer. Think GOOG411 -- a great way to collect voice samples.