"On the question of interoperability, APIs will be the answer"
http://www.informationweek.com/news/government/technology/showArticle.jhtml?articleID=218400025
APIs are indeed how Cloud Computing platforms can link together. But it would be a mistake to think that APIs imply that programming is needed also. Infrastructural products like Vordel's Gateway Cloud Edition allow applications to link to Cloud services, and Cloud services to link to other Cloud services, using APIs but without coding. APIs are one part of the solution, for sure, but the ability to monitor Cloud usage, to apply policies to Cloud services, and to alert on outages are also vital. These are not delivered by APIs alone, but they are the mainstay of Gateway products which have been doing this for similar API-based integration for many years now.
Here is a screenshot of the configuration for linking a local Web Service to an Amazon SQS service using Vordel's Gateway. It uses APIs under the hood, but the configuration does not involve coding, and is just drag-and-drop. The policy governance, monitoring, and visibility is all provided as standard:
