A shorter (timelapse) version of this video without explanations can be found here:
vimeo.com/10715723

This is a tutorial version of this video about a script that allows sketching meshes using the grease pencil. It can be used to sketch meshes from the ground up or also for doing retopo.

Download the script:
4shared.com/file/257533626/ad5447f4/surface_sketching_v0_8_Beta.html

UPDATE 25-May-2010:
Hamish made a transcription of this video with each step explained in a PDF file. For those who prefer a step by step explanation in text format instead of going back and forth with a video, will find this PDF file useful:
4shared.com/document/PKngvYeH/SurfaceSketching_videotutorial.html

Tested with Blender 2.5 revision 27974.
Find a fresh Blender version at
graphicall.org/

Blenderartists forum thread:
blenderartists.org/forum/showthread.php?t=183863

Some known issues as for v0.8 Beta:
- The object being sketched must be in location X=0, Y=0, Z=0.
- If there are no strokes and hit "Add surface" the object may be duplicated.
- The surface is first done as a separate object and then joined, and a "Remove Doubles" is performed to attach the mesh. This will likely change in the future, but in the meantime be aware of that remove doubles if you don't want it to performed on your mesh.

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