But can you hold the API to the SLA? »

Great article by Jonathon Feldman in Information Week recently with some steps for CIOs to take before getting into cloud computing.   One is to insist on SLAs from cloud providers, especially considering the natural tension from the provider's perspective between high-availability and low-cost operations.

Absolutely agree.  But to build on this - remember that scene from Seinfeld where Jerry is at the car rental counter -  "Anybody can *take* a reservation, the important part is to *hold* the reservation."

Often, cloud and API providers will agree to SLAs, but have limited means to enforce or verify the SLA is held. Many SLAs are just 'on paper' with minimal enforcement or monitoring.  This gets especially tricky if you need to discuss financial penalties. 

Consider how you will monitor, meter, and audit API traffic and content between you and your partners - from your side - in order to pinpoint problems, protect your organization, and especially if you need to enforce penalties based on SLA misses.