I joined a service called LaLa where users list music cds that they
want and also ones that they have and would like to get rid of. LaLa
matches haves and have-nots and sets up a system where you can
semi-anonymously send your cd to the person who wants it, and for
every one you send, you get one from your wantlist in return.
What makes this relevant to mail art is the reusable plastic cd-shaped
shells that LaLa provides for you to put the disc in. I received one
last night that had several pieces of art drawn on it with different
colored Sharpies, one from each of the people who had the plastic
shell before putting in their cd and sending it on again. Each person
who had added to the art on the case put the name of their hometown.