For several years, this day used to mean worldwide damage caused by the CIH virus. This virus was very widespready during 1998-2000. It was programmed to activate destructively every year on this date, overwriting most of the data on the hard drive and attempting to overwrite the Flash BIOS chip of the computer, making it unbootable.
The CIH virus family is no longer widespread. Last time we saw significant amount of damage (mostly in Asia) was in April 2001. We expect to see no damage now in April 2004.