I have watched the growth of Cloud-mania and although I do think it is part hype ala the lexicon de jeur, that doesn't mean it isn't a really big deal. Service based computing offers so many solutions to so many problems. In many ways it is the obvious destination. That said, it is not without significant hurdles.
Today's cloud adoption seems to be all or none, lacking in the federated nature that was called out as critical to further growth. To really get there IT needs to be able to move data and code ( containers ) fluidly into the cloud and maintain performant and secure communication with these containers. Furthermore containers need to be mutually exclusive, where no data can touch another container. These containers must also be safe from denial of service. No hostile container can take their resources or block their access. Isolation and communication are both critical, and will sometimes be at odds...
Because of this need, I believe the sensitive ( business critical ) solutions will first be realized as "Private Clouds" . Using the frameworks being defined by the cloudbuilder forum IT can gain the expertise needed to move forward with Utility "as a service" clouds. Companies getting the expertise today will be among the first to take full advantage of utility/service/cloud computing. This will give them a cost and performance advantage that may put the late adopters in jeopardy.
I sort of doubt we will be calling them clouds in 20 years, but my guess is most of the processing in the world will live there by then.