Here's a quick one:
I never previously saw a whole lot of value in the "blackout" and "whiteout" functions in Powerpoint. For those of you not familiar, pressing "B" or "W" while in presentation mode in Powerpoint will turn the screen black or white, respectively. During my MSDN Event in Appleton, WI, I had a spontaneous motivation to get everyone's attention back on the event following a break by using the blackout function to "flash the lights", much like after intermission at the theatre or symphony. It seemed to work very well, as everyone immediately looked up and then filed back to their seats.
Just a handy tip for all you professional (or aspiring) presenters.