To go along with the tradition of April Fools, a few people in my office have pulled minor pranks throughout the day. Basically, if you leave your desk you are bound to find something odd when you get back.
After returning to lunch, I found that my mouse did not work so I turned it over and found a pink post-it claiming "April Fools!" that covered the laser.
Calendars have been changed to 2007 and months switched, ring tones have increased and turned to the most annoying sounding ones, chairs have been manipulated to fall down, etc.
Minor pranks, a good amount of spice to lighten up the office.