I've found that many PowerPoint users don't know any useful keyboard shortcuts and always have to fiddle around with the mouse to start the presentation. It's also fun to watch people stepping back through a lengthy presentation to get to slide number X, going through all the animations backwards etc...
Among the best shortcuts I've found so far are
. to blank the screen to black
, to blank the screen to white
1 2 Enter to jump to slide number 12
In Editing mode
Shift F5 to start the presentation from the current slide (as opposed to F5 that always starts at slide number 1)
but I guess there are a lot more that I haven't found yet. What do you use?