With a single card costing just under $3 USD, this isn't an API I think I'll be playing around with until I've got a really good idea, but I can't wait to actually come up with something good.
My current idea is a bit arty, something like: style for a month.
For 30 days, each day, scrape yesterday's image from http://theimpossiblecool.tumblr.com/ or http://thesartorialist.blogspot.com/ (or just pick one at random) and use the API to mail it myself. Eventually, I'll be getting a postcard a card of cool style and get a cool physical collection.
I've seen this similarly with Flickr: email me each day with a photo I took 1 year ago (or some random old photo I took), so you always filtering through your old collection. But maybe postcards will feel differently.
