Christmas card etiquette?

[GoodyGoodyGumdrops]

If someone sends or gives you a Christmas card, do you have to send or give them one?

No of course you don't have to.. do you want to?

I'm not bothered. Don't see the point in giving them to people you see regularly - they should be for people you don't see and so can't say Merry Christmas to in person.

But I've received one in the post, and I've no idea who it's from, and don't want to offend anyone!