I don't know AutoCAD, but I do know the materials Shapeways offers.
As a general rule of thumb, aim for faces on curves that are half the minimum detail size. i.e. A 2mm diameter cylinder printed in WSF, 60 edges around the circumference and 1 edge for the height ( = 120 triangular faces for the cylinder walls) this works out to be just over 0.1mm edges on the curved areas. (with FUD, aim for 0.05mm)
The limit for (regular) upload is 1 million triangles, surfaces constrained to the regular axis of a model should be ok at whatever size triangle, however surfaces that transistion from one axis to another or are on a diagonal need to be pretty detailed to avoid 'printer stepping'... so the more triangles you can get into your model the more accurate the final print will be to your model.
Paul
[edit] sorry, I forgot my manners. Welcome to Shapeways!
A handy tip when modelling, turn off all smoothing - smoothing is a visual thing for us human-beans, printers cannot see
Last edited: Jan 22, 2012