Graphite Drawing now has support for undoing changes. However, there is still plenty to do. Here is a list of features that I hope Graphite will have soon:

realistic pencil strokes which vary in strength depending on how fast the user moves their mouse/finger

allow switching between different tools (pencil, eraser, paintbrush, etc.)

opening and saving files from and to local storage and Ubuntu One

events view for listing sketches by date

sharing through social networks

storing sketches in sketchbooks

Feel free to download the source code at the Graphite Github repository.

Anything you wish to see in Graphite? Comment below.