I've taken to printing the top of Wizard's jewelry box as a good way of testing surface finish, since it is a demanding shape that shows up many of the difficulties, without taking too long to print.

The image shows me arriving at better Skeinforge settings for my Cupcake CNC with Mk5 plastruder, derived from sideburn's suggestions here: http://tinyurl.com/23dxxyb

Carve
.35 layer thickness
1.7 Width/Thickness

Speed
30 Feedrate
230 Flowrate

Which gives a dramatic improvement in surface finish, while keeping the print layers adhering to each other. Note that these settings will be somewhat different for different bots/extruders, even ones with the same equipment.