A funny easter egg I recently came across in Windows XP, relating to files created in the future:

  1. Set your system clock to a date in the future (something far in the future; eg December 2030).
  2. Create a new file (anything, a blank text document will do).
  3. Set the system clock back to the real date.
  4. Open the directory containing the newly-created file.
  5. Choose the View → Arrange Icons By → Modified option.
  6. Tick View → Arrange Icons → Show in Groups.
  7. Look at the group heading of the newly-created file:
    Windows XP Easter Egg - “Sometime This Millenia”

Of course, that should be "Millenium"... Millennia is plural :P