thanks, your suggestions helped. The Host key is indeed the 'entry' for bringing Cmd+Tab to work to switch to to any other app outside the VM under Mac OS.
Your were partially correct on what Expose is. While Cmd+Tab gives you thumbnails of every open application to switch to it, Expose scales down all open windows to fit your screen. It basically is the difference between wanting to switch to a particular app and to particular open window (in case an app has several open windows).
While it your suggetions help I would nevertheless call on the developers to streamline the experience for Mac users - meaning to bring it to work without a 'trick' or work around and to have the keyboard working as in any other app under Mac OS. In detail:
a) enable Cmd+Tab to switch to different apps outside of the VM (again while your suggestion helps as work around, this little trick was enough for me to have to bother the forum on this
b) enable Expose. Currently, the situation on this is somewhat inconsistent because sometimes I can activate it with my mouse and the Mac OS feature of Active Screen Corners and sometimes I cannot.
c) enable predefined hot keys of Mac OS - which on my configuration include the Expose and the Dashboard.
I realized that pressing the Host key can be work around for all of these, but the situation is very much inconsistent. I encounter situations where I do not need to press it, where pressing it one time does the trick, then again I need to press it two times before the mouse gesture of the Mac OS hotkey are accepted. All these situations have happened.
I currently do not know why. I have worked now two minutes where everything seemed to be streamlined without having to press the Host key and now I am back to the 'mode' where the host key needs to be pressed before.