Like Hillary Clinton, you can use it to keep lists of your friends and enemies.
But for most people Excel is used for number crunching. Abbott Katz runs the spreadsheetjournalism blog where he creates all kinds of Excel wizardry on subjects as diverse as baby names, London underground lines and left-handedness. Wittily written, it's a great read if you enjoy getting the most out of Excel.
(But don't forget about the many disasters that are possible from misuse of Excel. You might not have heard about the last item in this article.)