Excellent app, even better than I expected. I used Brackup to back up 55 GB of data (200k+ files) to Amazon S3, and to keep it in sync weekly. It took a while to find all the dependencies needed on my debian stable linux system but was well worth it in the end.
The previous review doesn't make any sense -- Brackup is an application, not a general-purpose library, and is documented like an application ("why was it written", "how do you use it" -- not "what's the public interface to this class"). I don't know how you'd be able to do anything with it without discovering that, since even the synopsis for Brackup.pm shows you a commandline and not any Perl at all.
And at that it's an awfully useful application, which exactly solved a problem I had: remote backups somewhere you have a lot of space but no privacy.
There's a bit to go before a 1.0 release, especially in the number of supported backup targets (filesystem is doable, but I'd rather just scp the chunks around), but it's a turnkey remote-backup solution otherwise.