UPDATE: The DTV Coupon Program officially ended on July 31, 2009. Further information regarding background and statistics can be found at at the Department of Commerce's National Telecommunications and Information Administration (NTIA) web site.
On February 17, 2009, the television stations that broadcast analog signals over the air will be required to switch to digital. You don't need to worry about this unless you currently use a roof antenna or "rabbit ears" on your television to view TV.