I would like to see some basic documentation for every effect in Inkscape telling: - what state Inkscape must be in for the effect to be successful - how the effect responds to errors - what changes to the document result from the effect - dependencies of the effect (language, additional libraries)
A wiki seems like it's a good place to start for this documentation. Someone has already started a page for this here: http://wiki.inkscape.org/wiki/index.php/WhatEffectsDo, and I have added one more example. I was going to attempt this on my own, but I thought I'd do a callout to the developers first because they know what their effects do better than I do, and when I was effects code on the SVN some of it wasn't documented much.
Thanks for effecting,
--Justin