I really think it's such a shame that people aren't sending Christmas cards anymore. We're all getting so far removed from each other with our busy lives, no one has time for anyone else anymore. I like sending cards, I like thinking of each person as I write them, and I love to receive them too. It's a tangible connection to other people, and that's getting lost... in my opinion.
As a PP has said, by buying charity cards you are giving to charity, and you can also give a donation to charity as well. I also don't see any problem with supporting the post office - a great service which we need to hold onto!