I dunno... I've been selling T-shirts online for four years now.  That, along with cards, keychains, bags, playing cards, iPhone cases, etc.  With more than 37,000 products for sale, it's unusual if I don't sell multiple items per day.  My BitcoinLove store is now at about 261 products, but there's only a couple of basic designs so far.  My math and technology related products usually sell pretty well... I don't see why Bitcoin related products won't do well either, especially as the coins gain more acceptance and popularity.