I have contributed to numerous studies on why I am not moving my infrastructure wholesale to the cloud - but no-one appears to actively RATE the answers provided: I do flag up security, because it is an issue currently, but it could be managed away. There are three* reasons, and only three* why I'm still not going to hop on board this hype train (yet):
1 - Information Management
2 - Cost*
3 - Connectivity/Bandwidth/Service
1 - Information Management - moving to cloud would utterly destroy our ability to control our Information Management policy, and Office365+Sharepoint would drive a coach and 4 through any excuse for a controlled document repository - essential for Government related organisations.
2 - cost*: it is substantially more cost effective for me to to leverage existing investment in rooms, hardware and skills, and will remain so as I'd have to go cloud for everything ALL AT ONCE due to the interrelationship between all our systems.
3 - Connectivity/bandwidth/service: I really do not want to have to extend my hops from client to server, increasing latency and creating a chain of new single points of failure ALL OF WHICH are outwith my control, and at the end of expensive bandwidth (organisation size/location dependent).
* - bonus cost point - for my main job it is still cheaper to buy hardware, licences and cost operater time for (example) Exchange than use a cloudy solution - this is extrememly sensitive to organisation size however, and one smaller org I manage is now firmly "in the cloud" because the reverse was true for them!