But, I want to emphasize (since it back my opinion) 2 points:
    1. In one hand, some concerns about public cloud security are starting to fade, as it’s showed in this infographic when comparing the results of 2012 survey with the 2011 one. Of course, security concerns still remain high, but they are changing from infrastructure technology based security risks to laws and standard compliance related subjects what shows are higher confidence in the Cloud Service Provider and the solutions they use to offer their service.
    2. In the other hand other concerns are growing, as also showed in the picture (compliance, loss of control, complexity, and so on); however, in my opinion two of the more important: lack of standardization (and its several consequences as vendor lock-in, no interoperability, and so on), and weak SLA are missed (according to the data of the survey that this infographic summarizes survey).

Note: About SLA, I should mention specially the one related to service unavailability, since according to International Working Group on Cloud Computing Resiliency, each year a cloud computing is usually down for an average of 7.5 hours. And yes, I know that availability and other SLA measures security properties (see my post titled “Cloud SLAs: a technical point of view“).
 
(Note: the source of this infographic could be found here: http://www.andrewhay.ca/archives/2224).
 
Cloud_security_Survey_2012-infographic