While I am typically not creative enough to come up with any really outstanding April Fools Jokes, I appreciate a well-thought out prank. I have to say the Google prank (Gmail Custom Time) is pretty funny. Not overly believable, although when I was working full-time I would have LOVED this option. If you're in the mood for some good geeky humor, visit http://mail.google.com/mail/help/customtime/index.html
Otherwise, Happy April Fools Day!