Apple treats the feature like a bastard step-child who it is illegal to let starve. They used to have lots of information available through their API, such as which Space was active, which Space a window was open in, etc. and a few developers were beginning to make effective use of that, then Apple deprecated everything. The only API that is still publicly available is NSNotifyActiveSpaceDidChange, which Peter has made available (thanks!) in KBM as of v11.0.