A great post in CIO.com from Bernard Golden about Cloud provider SLAs.   Reading his post reinforces the importance of Cloud architecture in your implementation and also the structure of your SLA with your Cloud services provider.

"SLAs don't provide much protection against cloud-related outages, writes CIO.com blogger Bernard Golden. They merely credit customers against the cost of a service. To prevent outages, IT departments would better spend their time planning application architectures rather than duking it out with their cloud computing providers over SLAs." 

For all of the advantages Cloud brings, it takes a comprehensive strategy, architecture and vendor relationship to insure it's successful implementation and use.