Illustrator CS4 introduces the Blob Brush tool.
The Blob Brush combines between the pencil tool and the Outline Stroke command (Object>Path>Outline Stroke)
Blob Brush - tool options.
Double click on the tool and you get a world of new possibilities, here is what all these options mean:
Keep Selected – when you use this option, what ever you draw will remain selected even after you stopped pressing the mouse down.
Selection Limits Merge – if what you draw using this tool has the same Fill properties as other object in the document, they will merge together.
Fidelity – This option determines the distance between anchor points, which are created as you draw. The larger the value of your Fidelity the smoother the objects created.
Smoothness – Refers to the smoothness of the object’s strokes, this options is best used on shapes that are not finely detailed.
Size – Determines the Brush size.
Angle – Determines the Brush angle.