Blosxom Plug-In: interpolate_fancy
Rael Dornfest: The first plugin I'll be writing using interpolate_fancy is for atom (or whatever it's called a few minutes from now).
I must say that it was a joy to create this plugin. I had nearly forgotten how much fun Blosxom was.
Something to consider: it might be helpful to have a way to call a Perl sub defined in a plugin from within a template. This would enable one to create logic that is only needed in order to support some specific plugins.