That MAY be the case (I'd love for a number of independent parties auditing the security, NOT paid for by AgileBits), but it's still a single point of failure. What if they have data loss? What if that data loss causes local data to be lost due to a sync operation?
I've always used the Dropbox approach + backups. If Dropbox has an outage the file is still synced locally. If Dropbox deletes the file via a sync operation I still have my backups. If I delete the files Dropbox has an undelete option.
All I want is control over the files.