I never do. Haven't for years. Some years I buy them and intend to but I never do. A couple of times I've even written them but not got around to posting. The only one I send is to my mum (and I send her a parcel anyway) because the one year I didn't she sulked about it for weeks.
Every year when the nice cards arrive from all our friends I feel guilty - but not guilty enough to actually sit down and write cards. I wouldn't care if we didn't get any and I think it's a waste of time and money and card at a hugely busy time of year so it never ends up happening. I'm not sure if anyone has ever noticed. I think if I had not had a return card as many times as our friends have not had a return card, I'd stop sending to me, so maybe they haven't noticed...
Am I an awful person?