I sketch a cartoon (with the mouse) and I like to use the single path line (pencil) tool to do it -- mainly because I can clean the lines quickly. If I use the calligraphy tool it;'s nice, but hard to tweak.
I have found that the freehand line tool in Sodipodi actually works far better for this. It has a "weight", a slowness to it that produces fantastic lines and curves and with only a few nodes to tweak.
Maybe another solution could be just to use the "Simplify" command (Ctrl-L) to reduce the number of nodes of your lines after you've drawn them.
I end-up having to do that. It's hard to get a "controlled sketch" look with the pencil tool without having some form of "weight" to the tip of the pencil. In the end, I draw a rough shape and then go into node-edit and tweak and reduce and so on. It breaks the flow of drawing, but there seems to be no other option.
Really, if you can install sodipodi (it's in the Ubuntu repos) -- try out the pencil tool; it's marvelous!
/d