The Filesystem target works now, and the DigestDatabase works. Haven't yet done Amazon, but Leon (cudddly) did the hard work yesterday, so I just have to plop in Net::Amazon::S3 and I'm good to go.
Last part is serializing the metafile (the finished backup file you need to do a restore). Was going to use YAML, but YAML in Perl sucks, then maybe XML because Net::Amazon::S3 uses LibXML, but XML, really? Bleh. So now I'm leaning towards old-skool RFC-822 format. If it's good enough for Debian, right?
I should've finished tonight. Want to get back to DJabberd.