Cutting a part into two objects using a plane I'm still way down on Blender 2.72 learning curve. I've tried to get an answer just working with a basic cube and a plane and I'm not getting the expected result.

Object mode>select cube>shift select plane>modifier (boolean difference)> select cube (again)>apply
At this point, I would expect to see three objects: two pieces of the cube and the plane.  However the plane is apparently fused to a piece of the cube and the other object is the original cube.
Accepting this result and another bunch of commands and I might get to my result.  Do I really need to do this?  Have I overlooked a very simple answer?
BTW, I'm expecting the two pieces of the cube to be manifold.

I've spent a lot of time searching, but I can't seem to find the magic keywords or phrasing.
Partial answer: Don't select both the cube and the plane before going to the modifier.  Select the cube, specify the boolean modifier, specify difference, select plane, then apply.
This results in a part of the original cube (depending on the normals of the plane?) and the plane as the two surviving objects.  I would expect this result if I had started with a cube and another smaller cube and done a difference or an intersection. In other words, slicing with a plane (0 thickness) shouldn't result in loss of the original volume.