Great news! The Karmic Koala has just arrived and I like the new version very much. The coolest thing however is that now you can install RedNotebook directly from the new Software-Center or on the command line just by typing:
sudo apt-get install rednotebook
Unfortunately Ubuntu doesn’t always ship the latest versions of some packages. In Karmic you find RedNotebook version 0.8.1. If you want to get a newer version, follow the instructions here to add the new Karmic repository.
Have a nice day!