I feel that Bob is correct here, and that perhaps I should clarify my views a bit, if I can. I think that it is important to remember that there is a certain commitment when you join an exchange to complete your part of the bargain, and sometimes people will get upset if you don't. My default position is to give people a break, but since people do contact me about people who did not send cards, I have to attempt to find a middle ground. My main goal here is to try to make sure that everyone feels welcome to participate in the Postcard Exchange, doesn't feel heavily pressured if they are running behind. I would ask two things: one, that if you are going to be late that you please let us know so that everyone understands the situation - most people are quite understanding as long as they are not left in the dark - and two, that you sign up for an amount that you think you can do without undue stress, so that you can enjoy the exchange and still be able to send your cards so that others may enjoy the exchange too.
I know I've missed the deadline a few times <cough> for other exchanges, both on and off APUG, at one time or another, so I understand what it's like to be in that spot. That's why I put in the initial post about not being able to participate again until you have mailed your cards. If you can get caught up, please do, but I will not pester you via email or PM about it - I will simply not include you in the next round until you get caught up.
I hope that by both allowing people to print fewer cards and limiting the exchange to people that have completed the previous round that we will get to a point where only the cards on 'postal vacations' will be unseen. Lastly, I would also encourage anyone who does not get a card from someone in particular to contact them about it, as cards *do* get lost in the mail from time to time - they can get torn or jammed in machinery and, while the postal services of the world try to do a good job, they do have the occasional problem with small, thin pieces of mail like a postcard.
Thanks for all who have joined, and to those who have sent cards in the past. And, please, feel free to contact me to voice your opinion, good or bad on anything I've posted here (especialy the bad, because there is often a lot to be learned from criticism...)