Hi Mo,

re:
> Although, I had a problem on some extruded surfaces.
> I extruded an "S shape" curve, and this is the result:

Stepping by even distance amounts in parameter space does not necessarily yield even distances in 3D space, the parameter space may be squished or stretched in relation to 3D space. For an extrusion if you had uneven spacing in the control points of the curve being extruded that will have that type of squishing or stretching in it.

A rebuilt curve will have what is called an "arc length parameterization" which means the parameter space is in sync with 3D distances. The Network solved it because it implicitly does a rebuild on its input curves. If you ran Rebuild on your curve before extruding it that would also do it.

- Michael