There has been a number of recent developments in the world of introspection, let me summarize some of them:
Gjs has recently gained callback support, which has been kind of a personal pet peeve for me. Making sure that functions and methods with callbacks are possible to call from a language binding has always been difficult. GClosure sort of solves that problem, unfortunately very few libraries actually use them. Most of the tricky work of landing callback support in Gjs was done by Maxim Ermilov, rock on!
The Python bindings are also moving along pretty quickly. Tomeu Vizoso and Simon Van Der Linden has been working aggressively on making them solid. The rumor tells me that Tomeu has the whole OLPC Sugar interface running on top the new bindings, with significant speed and memory improvments!
Elliot Smith at Intel blogged about his experiences on using Gjs on Moblin developing a clutter application. Zach Goldberg writes about his experiences on adding callback support to the python bindings.
More and more libraries are adding introspection support, the latest ones are libgda and moblin toolkit.