Hi Marco,

> "2D curves that are all on a single plane will generate a curve result,.."

That's for the Boolean intersection command, where you can do something like boolean 2 circles that cross each other like this:



But the command Felix is talking about is actually not the boolean command, but the "create intersection curve" command which is under Construct > Curve > Isect :



This command is a separate function from the booleans - unlike the booleans it does not try to edit a shape by removing pieces from it, it is about generating curves where surfaces intersect each other. It can also can also generate the intersection curve between 2 perpendicular profile curves, basically by internally extruding them and intersecting the extrusions. There's an example here:
http://moi3d.com/2.0/docs/moi_command_reference7.htm#intersect

- Michael