VALENTINISSIMO  Mathusalem answers all my wishes for a back-up solution: Tested it with 600 MB worth of data sent to iDisk, S3 and to external disk and all three work like a charm. I especially like the way the retrieve function was designed. I had to do some experimenting with different settings because the documentation is not as good as with a commercial product. On the other hand you get a very little intrusive piece of software which works quite intuively.   
(Version 1.5)