It sounds like you have it covered, but why not use a service like Dropbox or Tarsnap that backs out to Amazon S3 where they have like nine 9's of redundancy?
Backing up to the cloud is the next big step in backup.
Backing up to the cloud is the next big step in backup.
The only answer I see is "they want to do something nefarious." Otherwise there would be a simple web interface for people for which that is enough. Or even a simple html based API.
Is Tarsnap better?
(2) Their app adds a huge value, in that it automatically uploads any changes to files in your local Dropbox folder. It is convenience, and hardly nefarious. Everything that can be done to make backups easier and more automatic is a good thing, IMHO.
If you don't want the automation, then yes, another solution is probably better.