Hi Raven, for it to take on the characteristics of the surface it means that the surface has to be actually cut up - I don't expect to have that part included directly in the Extrude enhancement stuff that I've been talking about but it would be a part of the "limit depth" option in the booleans though. Well, maybe it's possible for extrude as well, I'll think about that some.

You can actually have Extrude work like that currently though if you cut the base surface up using Trim - you can also extrude individual surfaces, not just curves. See here for an example: http://moi3d.com/forum/index.php?webtag=MOI&msg=3024.4

There are 2 different ways you can thicken an individual surface like that into a solid currently - Extrude will make an object that goes out straight in one single direction, while Offset > Shell thickens an object by doing an offset operation which makes the other side follow the shape of the surface staying perpendicular to the surface at every individual piece of it (more like a "slab of even thickness everywhere" which is different than an extrusion shape).

See here for a comparison of Extrusion versus Shell and the different results that they make when thickening a surface into a solid:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4791.13

- Michael