Inkscape is an extremely powerful tool. I’ve played with the lib2geom code which is the underlying representation of paths and shapes used in Inkscape. I think a small fraction of the power of this API is exposed through the graphical interface. The following is a quick guide to smoothing a freehand path in Inkscape. The correct term for this in the tool is “simplification”. This is inherited from the lib2geom API.
First, choose the draw freehand tool.
Then, secondly draw some kind of path.
Finally, with the contour highlighted press “Ctrl+L” i.e. hold down the Ctrl key and the L key. Alternatively, choose “Path” from the menus and “Simplify”. You may need to simplify the path a lot to see a visual difference. Here’s the above path after I hit “Ctrl+L” about ten times
And we’re done 
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Great – saves me loads of time
Yay! Now it looks like I used a graphics tablet!
Since Inkscape 0.47, the freehand tool has its own smoothing option on the tool controls bar: set the slider between 30-50 and you barely need to apply ‘Simplify’ at all (minor corrections then are more easily done using the node tool imho).