I've been testing the Custom Post Type List Shortcode plugin by Blackbird Interactive (available from the WP.org plugin library) with MarketPress. It has many more attributes than MarketPress's own mp_list_products shortcode, and thus is a lot more versatile. One (significant) problem I've run into, however, is that its category attribute doesn't work -- whenever I use it, I get a "no products found" error. I've contacted the author about this, but no response as yet. So I wonder if anyone else is using this otherwise very handy plugin with MarketPress, and if they are having any success with the category attribute. Or, perhaps, if anyone can suggest why this one attribute doesn't work, in contrast to the many others that do.