February 17, 2009
Why the switch?
DTV technology is more flexible and efficient than the current analog system. The switch to digital broadcasting will allow television stations to offer crystal-clear pictures and sound, plus more channels and programming – all for free. The Deficit Reduction Act of 2005 requires full-power television stations to turn off their analog channels by February 17, 2009 and begin broadcasting exclusively in a digital format.
Going all-digital will free up parts of the airwaves for future innovative services by entrepreneurs. TV stations can also improve their services with enhanced closed captioning, better pictures and sound, and offer several channels of programming at the same time, known as "multicasting."
Today, 1,631 out of 1,760 full-power television stations nationwide already offer digital programming in every market in America. To see if your local station currently broadcasts in digital, click here.
from dtv answers website and if i remember correctly it will also free up more airwaves for emergency services such as 911