We have gotten around to adding support for JSON output when using the "Advanced Method" API. The default will remain as XML, but you may pass &stwadv=json to get a JSON response instead.
The integrations and sample code will not support JSON for awhile, until we get caught up enough to add that update to the list.
Please refer to the ShrinkTheWeb Documentation for details and sample JSON responses.
You may also search for "json" at http://support.shrinktheweb.com to find some sample JSON responses.
For those who try out this format, please let us know if you find anything not quite working as you expect.