Re: Columbia
Looks more and more like the "tire blowing off the wheel well door" theory is gaining ground. Debris at launch may have hit and deformed the door, causing a slight crack in whatever seal is used to keep the hot gases out of the wheel well. A piece of space debris punching a hole in the Shuttle may also be a candidate. I really think they will nail it down exactly if they find enough debris.
That gun camera shot of the Shuttle's disintegration on the page you linked to is also very interesting.