As a followup to my comment about people treating my Moo cards a bit like trading cards, I've found out that there is the Moo Me Flickr Group dedicated to... trading Moo cards (Flickr's note feature seems particularly well geared for supporting this style of interaction)). I even found this well-done notecard specially designed for Moo card trading. Maybe I'll trade a couple if there happens to be a cycling fan amongst them.