The comparison of Inkscape and Sodipodi freehand tools generates a heated debate. Here are two screenshots demonstrating different aspects of the problem. Feel free to upload your own examples with commentary.
1. This user uses a mouse and draws slowly, using small curved strokes. For him, Inkscape's handling of small curved strokes is inadequate; Inkscape generalizes such strokes too much distorting them. Sodipodi's tool is better in this situation.
http://bryceharrington.com/freehand_drawing.png (dead link, domains seems to be hijacked)
2. This user uses a tablet pen and draws pretty fast using long energetic strokes. For him, Inkscape's freehand works well, with the handwriting being recoignizable; Sodipodi's freehand lags behind intolerably, making handwriting impossible. Smoothness is good in both tools; the spiral drawn in Inkscape is both smooth and close to the actual hand movement. Sodipodi's spiral is also smooth but it is noticeably smaller than the actual pen movement because of the lag, i.e. a given shape is difficult to reproduce in Sodipodi unless you move your pen very slowly.
File:Freehand.png (someone should re-upload this image)