Jonathan Stark, author of Building iPhone Apps with HTML, CSS, and JavaScript, has not only posted his Starbucks card for all to see, but he’s using it to conduct an interesting experiment in social sharing:

Hi! I’m Jonathan Stark. You can download this picture of my Starbucks card to your phone and buy coffee at Starbucks with it. Seriously. My card gets charged, you don’t. Details are here.

If you’re feeling generous, you can also add money to my Starbucks card by doing this and enjoy some serious good karma.

Jonathan’s Card is an experiment in social sharing of physical goods using digital currency on mobile phones. I stumbled on the idea while doing research for a blog post about Broadcasting Mobile Currency.

Not only that, but he’s created an API for the card:

At least two fellow geeks built graphing apps on top of the @jonathanscard Twitter stream within the first couple of days. Rather than break apps every time I change the Twitter message format, I whipped up a simple read-only API that returns JSON.

Give a coffee, get a coffee – Jonathan’s Card
Developer API