The CSP is the small part of lock-in concerns. Transferring data between CSPs can be accomplished through a number of means, however certain techniques such as deduplication that gateway providers commonly employ is a far greater form of lock-in. Dedup techniques are proprietary and from a usability perspective, using it is the same as encrypting your data with a key only the vendor knows. It means you're forever required to use the gateway to access your content on the CSP. Unfortunate, because one of the biggest benefits of these storage platforms is the flexibility of using the API with any number of applications (be it a gateway to expose CIFS/NFS, for distribution through a CDN, big data processing using hadoop, etc.).