My ZDnet colleague, Ken Hess, published How will you secure The Cloud? yesterday. It was an interesting review of many important elements of a secure Cloud environments. I didn't see a mention of securing the data, however.
Several suppliers, including Nausani and Oxygencloud, just to name a few, are offering ways to safely and securely use Cloud storage. The data is encrypted as it leaves the organization's data center.
Some products keep the directory in the organization's data center and only put data elements in The Cloud. It would be very difficult to make sense of the encrypted data even if portions of it fall into the hands of the wrong people.