Just a heads up that I'm dropping quite a bit of new code on the tree tonight; I've been rewriting more code to take advantage of the garbage collector, and in the process I ended up gutting and rewriting the GC wrapper API.
To summarize real quickly:
Inkscape::GC::Object<> -> Inkscape::GC::Managed<> Inkscape::GC::FinalizedObject<> -> Inkscape::GC::Finalized Inkscape::Refcounted -> Inkscape::GC::Anchored
Inkscape::Refcounted::claim() -> Inkscape::GC::anchor() Inkscape::Refcounted::release() -> Inkscape::GC::release()
One important change is that the three GC classes no longer inherit from one another. So you will need to derive from Managed<>, and then also from Finalized or Anchored if you require features added by either one of those classes.
-mental