hi there,
i was wondering about this issue as well. I couldn't decide whether giving christmas cards just looks desperate, inasmuch as you're giving them out simply to recieve tips in return. the same goes to wearing a christmas hat (you know the ones; red with white piping) as if to say "don't forget, it's christmas, so tip me!". i personally haven't given any out this year because i believe customers pay me because of the service and attitude i offer all year round, rather than a card given out at the end of the year.
cheers, matt