I saw one in person at the Maker Faire. It made very neat prints on paper. It does have some limitations on trace size and current capacity, but it's fantastic as a learning tool and works great for logic and older SMT.
I've also seen articles and pictures of the conductive/resistive/N-Type/P-Type silicon ink(+3d) printers as well. That category is being temporarily referred to as 6d printers to distinguish it from the current run of 3d and SLA types.