I made the addon back during Burning Crusade because for my fire mage, I hated sifting through a few pages for 5 spells. Then, it was made obsolete in Wrath of the Lich King, which was not a bad thing.
My primary objective for this addon was to make the Spellbook better.
So far, this addon filters the Spellbook to the latest rank of each spell, has a basic auto-update when new spells of a higher rank are learned, and a way to highlight stance/form specific spells.
I am open to suggestions for other improvements. My next thought for an addition is a way to add spells to a "favorites" list that would be in one of the unused skill line tabs.
Another note, I have the Spellbook close and stay close during combat due to some functions used to update the spellbook in Blizzard's code are restricted. I have an idea of how to get the Spellbook to work in combat again, but I don't see it as a priority. I am still trying to figure out how to make the restricted environment work in a simple method, not one that involves replacing 14 buttons.
Also, I am always suspect of bugs that I forgot to test.