Fantastic idea, great implementation, but I've got a couple caveats.
1. Need to be able to see "long" to-do's - i.e., as far as I've been able to test, typing in an item that is longer (wider) than the notebook is hidden from view.
Would like that to appear on the second line automatically. Currently you have to use the arrow keys or the mouse to edit the line and scroll sideways to see it.
2. Would like to change font/size
3. In response to #1, might be nice to add resize notebook ability.
All for now... keep up the good work.