The clunkiness of the Gui Controls compared to a native windows interface is very apparent, especially in their response speed. The externally scripted windows will go a long way in creating enthusiasm for developing scripted tools for development which are sorely needed; things like a level editor with layering support and image-reading enhancements to GraalShop.
I'm sure creating support for external windows (to cover all the ends were things could go wrong) is not a simple task and I'm very grateful to Stefan for implementing it.