Every time I've had a need for "Undo" it has either not been available, didn't do anything noticeable (which worries me too), or had unexpected results. For example, I opened an existing presentation, changed the background on a slide but didn't like it, so I immediately did a ctrl-z. Nothing happened. I did a right click on the item in the service area, but Undo was not available. I have other instances where I have totally bollixed something up, but ctrl-z would not bail me out. When does it work and when does it not? Also what is the relationship of that little looping arrow in the upper right corner? That also has taken me down paths from which there is no return.
Thanks