This is a truely a sad day, this is worse than the Challenger disaster. Shuttle Columbia has disintegrated in the atmoshpere. It is looking like a heat shield failure as I look at the pictures. You can read more about this disaster at these numerous sources. This will be on your local news channel as well.
There are more, but CNN will be updated with the complete story as details come in. Columbia is the oldest space shuttle, and now, it is no more. My heart goes out to the families affected by the crash. If you are reading this and you live in northern Texas, please be careful of falling debris. This is truely a sad day.