There's three backup formats: XML (same as Delicious v1 API), HTML (legacy Netscape format almost everyone can read) and JSON.
I can get back with an XML file later. There's also an API that might be of interest.
Here's someone who blogged about that:
http://behindcompanies.com/2011/12/a-guide-to-backing-up-pin...
The question was asked if you can use your API endpoint URL (https://[pinboardusername]:[pinboardpassword]@api.pinboard.i...) straight into ifttt. Maciej confirmed that it should work, the problem is that you’re essentially storing your login credentials in a 3rd party service, and you don’t know if they’re storing and transmitting it securely.
https://gist.github.com/anonymous/316b9fd1108b026e116e91f134...