I belive that might not have been initially viable since part of their service is the mirroring of files that are already uploaded. If you and I both have the

I belive that might not have been initially viable since part of their service is the mirroring of files that are already uploaded. If you and I both have the same mp3 in our dropboxes, only one of us have to upload it initially, then the second person to add it would only have it 'synced' in their dropbox since the file checksum matches. If we both locally encrypted it with our own keys then the resulting file on the server would be different. It'd require more storage space and more bandwidth — more operating $. Maybe not though :-)