The way it works is you setup a MOO account, then allow it to access your Flickr photostream. Then you can select 1-100 photos to use for your cards. Once the photos have been selected you use their online cropping tool to select the area of the photo that will be printed. Next you ad some copy, like your contact info and so on, and then select the font and color of your choice. After that, you submit them to be printed and in about a week or so the cards will show up.
The print quality of the cards is suburb, with a really nice satin finish. They often draw a lot of attention when being handed out.
Also, their packaging is beautiful, with a lot of attention to detail. They come a tiny white plastic box that holds 100 cards, with a printed band to keep it closed and little shipping card showing the routing from London (LDN) to “Rest of World” (ROW).