For those of you who don't know what paubus is talking about, visit this link:
The synther uses the Photosynth webservice every single time that anyone creates a synth and yes it has been available for people to create mashups with since 2008 August 20 when Photosynth launched.
An example of a third party application that calls to the webservice is Christoph Hausner's SynthExport ( http://synthexport.codeplex.com/ ) which uses it to collect the point cloud files and JSON file for any particular collection (synth).
I believe that Greg Pascale's iSynth app ( http://www.cs.brown.edu/people/gpascale/iSynth/ ) also makes use of the webservice.
It is basically a way to get information about synths and to interact with them in some basic ways. Any web developer will know how to use the HTTP and SOAP requests.