If you’re in a powerpoint slideshow, and you press B, the screen will turn black. If you press B again, you’ll see the slide you were previously looking at.
HOW AWESOME IS THAT! You can actually have a powerpoint presentation for pictures or some other visual (maybe even a chart), and then BAM, blank screen so the audience can now focus on what you’re saying instead of getting blood shot eyes from staring at your amazingly lame slideshow – I don’t care how awesome you think your slideshow is, it’s most likely a distraction more than half the time, and a seriously annoying distraction at that with a side of eye strain.
Of course, the best powerpoint presentation ever is the tip that shows you how to turn it off.