This is a set of herringbone gears similar to http://www.thingiverse.com/thing:10538 but done entirely in openscad based loosely on http://www.thingiverse.com/thing:6544
*** UPDATED 25/12/2011 ***
uploaded my latest script which I've worked on a lot. It's generating some nice gears now.
Also updated the STL, ratio is 45:11, nut trap should fit perfectly straight off the bed now.
This is a detailed part (due to the tooth profiles) so use your smallest nozzle.
Print in PLA, it will last a lot longer due to being harder than ABS.
Set 0 extra shells (skeinforge)/ 1 perimeter (slic3r) because you can get hollow teeth with extra shells/perimeters.
Use 80-90% infill. I've already removed lots of plastic, what's left is what's needed. If your infill is too low, the most likely failure is the nut trap in the small gear will break.
You'll need really good cooling to do the base of the small gear properly. When the large gear is finished, crank your fan up to max, perhaps convince your slicer to slow it down a little too.