I like Notebook the way it is: simple and functional. I chose Notebook over the other in-game note addons out there because it has one single purpose, and does it well. It isn't cluttered with frivolous features like tacks and buttons. It just saves plain text in a nice, non-ugly window, and lets me send this plain text to chat.
My only "feature" requests are quite small:
1. Non-server-specific notes. One of my many uses for Notebook is to store my "group leader" speech about loot rules such. Another use is to keep track of bugs and wanted features for the many addons I use, in a central location. I don't mind editing saved variables, but while my loot rules might not change often, my addon note gets modified quite regularly, and all this manual copy/pasting takes away from my valuable WoW-playing time!
2. Add the Notebook window to the "special frames" list or whatever that is so it plays nicer with the other nice, non-ugly windows. i.e. if I have nothing open, Notebook opens in the normal window place. If I then open up the character pane, Notebook moves over into the second window place, or the character window opens there, or something. I don't know how well this would work with the movability though.