(sorry, video link is now dead)THIS THING IS FAMOUS! Shows up at 1:54 on this episode of Robot Hospital: http://www.youtube.com/watch?v=shpt1hD4z7Y
This thing can be used to see what your skeinforge settings and bot will do for certain wall thicknesses:
0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2
The OpenSCAD is included in case you want to try other thicknesses.
The image has the "as designed" thickness in green, the measured straight wall thickness "as printed" in red (for my bot, of course), and the measured cylinder thickness in purple.
My bot is set up with 0.25mm layer thickness and W/T of 2.0 for theoretical wall thickness or 0.5mm. For reference, I am using the MakerBot 0.4mm nozzle, but that really does not come into play.
Slightly related to: http://www.thingiverse.com/thing:7114
Just print and look at your output. Tweak and repeat!