Those looking at the convergence of SOA and cloud computing, including me, having just wrote a book on that topic, understand that the ability to find and leverage services, not infrastructure, out of the clouds will be the "killer solution pattern" for those looking to stand up an SOA, leveraging cloud-based services.
Programmable Web, and my good friend John Musser who runs that site, seems to have the secret sauce that many are seeking to link SOAs to Web-delivered APIs/services. John provides a directory of over 1,300 APIs that are ready and willing to be part of your SOA and/or mashup. It's just a matter of searching, understanding, and abstracting.
ProgrammableWeb is more than a directory and community, it's programmable.
Our "API for APIs" gives you a simple and structured way to access the powerful registry and repository capabilities of PW. Use your favorite language to search and retrieve APIs, mashups, and other data from our catalog.
Clearly, directories such as this, which are moving from visual to non-visual, or browser- to API-based, will drive more cloud adoption than Amazon and Salesforce.com combined, if you ask me. Those looking to modernize their architecture find that it's much easier to take API/service baby steps than adopt entire cloud-delivered infrastructures I would argue that there is some external service use within almost all commercial enterprises and government agencies out there, no matter if they are sanctioned or not. Can you say "Google Maps API?"
The funny thing about this movement is that it seems to happen behind the scenes. Also, while cloud computing is raging, few are talking about services/APIs in the context of the clouds. There is typically no input from the enterprise architect or IT for that matter. The need is there, the developer finds the service, and it becomes part of the application.
Going forward we need to consider these APIs as part of the SOA and, thus, part of the strategy. They are clearly a form of cloud computing, but their use within the enterprise is more about systemic evolutionary change than a big bang.