You send to everyone on the list and everyone sends a card to you. I've always had a few people that didn't send to me (not sure if it was the mail or personal reasons ) but it didn't ruin the fun.

Some people buy cards, some people make cards...most people include a photo of their pets or something like that. It does end up costing quite a bit by the time you are done buying cards and stamps, but it's worth it in my opinion!