Backup is irrelevant, you can always encrypt it and send to S3. As for safety, well, at least you're a considerably less visible and worthy target than Dropbox. And you can implement systems (e.g., stronger authentication) that Dropbox might disregard since they're targeting a less technical user base.

Personally, I use git-annex as my sync server, and all non-local transmissions are done over SSH using public key authentication, which is something that Dropbox will never implement.