in reply to On timely destruction?
I've seen Tk based scripts rely on this type of thing to trap window destruction. There's obviously better ways to do that, so I wouldn't call it a show stopper.
It might be worth polling the Tk community though, as they've had a pretty good history of complaining about GC :). ( regarding Tk's destroy vs DESTROY, and the underlying XS code hanging on to gobs of memory)