This YouTube link is worth clicking on! A guided tour of the Abracadada Rubber Stamp Museum from it's curator, William "Picasso" Gaglione. Founder of the original Stamp Francisco and now Stampland with his lovely wife, Darlene Domel, Picasso is extremely active in correspondence art.
My daughter and I were lucky enough to catch up with Picasso and Darlene in New York City this past June for a special exhibition, "Mapping Correspondence" at the Center for the Book Arts. http://www.centerforbookarts.org (look in the exhibit archives for Spring 2008 and check out the Flikr photos)
If you are interested in the history of rubber stamps, or just rubber stamps in general, check out this vintage video of the Abracadada Rubber Stamp Museum.