Although Garcon is used by a lot of core components, it is still an unstable-versioned package. The reason behind this is that we can still break the API without any problems in case we really need to.
Since the 4.10 xfce4-appfinder also heavily uses the Garcon library, we focused on performance of the library too. As part of this we discovered XfceRc was a lot faster then the more portable GKeyFile and there were also some inefficient loops in the code.
All these improvements are already in the 0.1.9 release, so maybe you already benefit from this with Xfce 4.8.
Completed: 100% (but always ongoing)