(Vaguely related to bug 97482 and 97483) [I have a dual screen system; in presentation mode, one shows full-screen the presentation, the other shows the presenter's view with current/next slide, notes etc.]
If I right click during slide show, I can choose "Mouse pointer as pen"; I can then also choose "Screen"->"white"/"black". If I then click the mouse, click+drag to draw something there, however, no drawing is shown, but as soon as I release the mouse button, the white/block screen is removed and the nonblanked slide is shown with the just drawn line.
Expected: It can be sometimes useful to make a sketch to question asked by the audience. Hence, it would be useful to have a blank screen (white piece of paper) for sketching something to answer the question. - Thus, the drawing should show up on the blanked screen and releasing should leave one in that mode.
In Microsoft Office, that's the case - and hitting ESC, clicking with the mouse (in arrow mode) on the screen, or clicking on Next/Previous in the menu, leaves the mode.
This sounds like a reasonable enhancement suggestion.
There are a few tricky parts to it, like what should happen with the drawing afterwards (currently if the presenter draws on a slide with "Mouse pointer as pen" turned on, the drawing remains on the slide afterwards offering the possibility to save it along with the presentation).