There's a new whitepaper up on the 3scale website - What is an API? Your guide to the Internet Business (R)evolution - definitely worth checking out. It's always tough to find the right metaphors to explain the value of APIs, so we've given it a shot.
Dion Hinchcliffe summarizes it best:
“We are nearing the time when opening our supply chains across the Web isn’t just a good idea, it will be essential for competitive survival"
A nice timely reminder since just a couple of days ago programmableweb crossed 3000 APIs in their directory - impressive and more to come no doubt!