Hi Burr, currently this new tool won't work in that situation because of the trimmed piece being flush with the surrounding surfaces.

Currently the borders of the piece are built by the intersections with neighboring surfaces - when pieces are smooth to one another they don't produce the right kind of intersections.

But you don't necessarily need this new command for that kind of a thing - you can use the current Shell command or extrusion on a trimmed out piece like that to thicken it into a solid, and then delete the front part of it.

See this for an example:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3024.4

That's not really too many steps for one part, but it would be nice to have it wrapped up to be more automatic, then you could do something like stick 50 circles all around an object and have them all make depressions with one command.

- Michael