I guess with Christmas cards, you actually are sending and receiving something, and they can of course be recycled. If they're from someone that knows you well and they've said something meaningful, then I see them as a nice thing.
Of course, if they've just got "Merry Christmas" in them or something quite short, I don't really see the point in sending them.
Here's an idea for next year.
Buy your friend a $5-20 pressie that they actually don't get. For example, $5 will get someone in Africa or similar locale a dose of vitamins for a few weeks. Your friend gets a card saying what the gift is, but the person in the developing nation actually gets the gift! It's sort of virtual reality meets reality. The best bit is, that it actually makes the world a better place.
Two catalogues that are good are the World Vision "Smiles" catalogue, and the Tear Australia "Arguably the World's Most Useful Gift" catalogue.
Here's a few links
http://trans.worldvision.com.au/Smil...px?source=1233
http://www.usefulgifts.org/
GK