By posting here I want to signal my interest in this topic as a geocaching-app developer (member of the c:geo team). As my personal interest in opencaching.de revitalised lately I was looking for ways to integrate it into c:geo.
I took a look at the xml-api. While it is sufficiently easy to use (it took me just a few hours to experimentally integrate it into search and live-map) its feature-set is not well suited for our app (e.g. no user-specific information on the cache like found and no write access), so I would like to ask for the state of things regarding OKAPI-integration (that we have already for the supporting sites) or what other possibilities exist for a seamless integration of opencaching.de into our app.