I am constantly amazed by the amount of work Andy Wingo puts into optimizing Guile, considering that I have never seen much uptake in Guile usage anywhere (which is a shame). It looks like he is doing more optimizations than some other, more popular interpreted languages do combined.
What was the latest interesting optimization in the CPython interpreter? Direct threading?
if guile emacs manages to become the default emacs that will be a nice chunk of users