Moo made a very big splash on Flickr when they gave users 20 custom-designed miniature business cards free of charge.
Flickr allows approved companies to access their database, so that Flickr users can pick and choose which photos to print on their cards - it is so easy to configure and the quality impressive enough that many people continue to order small batches of 100 cards at $20.
It appears now that they're trying to repeat this success with FT - I hope they make a go of it!