Hmm, sounds like tahoe may do what you want: http://allmydata.org/trac/tahoe
But like you I have also failed to get it to work on anything with any degree of success.
You mean that you tried to implement something on top of Tahoe, and it didn't work? Or Tahoe didn't work, so you went and wrote your own based on the Tahoe design? Or something else? :)
I'm sure that it isn't all there yet, and your bug reports would help, but you might be interested in the overall approach -- applying the principles of test driven development (if it isn't automatically tested by your buildbot, then it isn't done) to packaging.