John asked about the status of the PLT Scheme PLaneT source search system here; to which Jens replied here and referenced this post. This post has information about why you might want to use the search engine (find out where set! is abused!) and also links to all of his posts about the development of the engine itself.
Jens mentions that he is not able to focus on maintenance at the moment; but if anyone is interested he would be happy to pass them the code.