It's obvious that building an API is easier than 1) building and shipping physical devices that work well enough to qualify for card present transactions and 2)

It's obvious that building an API is easier than 1) building and shipping physical devices that work well enough to qualify for card present transactions and 2) obviating the need for a merchant account (only PayPal really gets you there, although Amazon Payments and Google Checkout kinda sorta do). Square decided to do the hard stuff first. And they pulled it off! That's what's so amazing about this company. I just hope that when they build their API that they do a PCI compliant vault that adheres to the Data Portability Standard. (Or, at the least, integrate with Recurly, who could handle the subscription logic and provide the PCI compliant vault.) And, of course, their chargeback management processes need to not suck. If they do, there would be no reason to ever, ever pick anything other than Square for any side project all the way up to a fairly large (>$100K/month) web app.