Along these lines, I've been thinking of a building a business around building APIs for small businesses. I'm thinking of local mom and pop grocery stores, local restaurants, my dry cleaner, my car wash guy, etc. Imagine a world where all businesses offered an API to interact with them.
While this is a fun--and potentially useful--idea, can I recommend you spend some time hanging around/working for small businesses? You'll find the experience pretty useful.
On one hand, you may discover (as I fear) that mom-and-pop don't need an API or don't have the resources to pay for one. Perhaps even if they did, nobody would use it.
On the other, you may conveniently find yourself with the first few customers you'll need. They'll already know and trust you, and you'll have very clear idea of what their challenges are.
Don't think API, think structured data in HTML. You could get all those benefits by just convincing the web developer to properly markup that information using RDFa or similar.
