Pat gets a no-prize by brining this NYTimes article (free reg, blah blah blah) summarizing the latest findings about the Columbia disaster. In the "dur" file comes the revelation that conductive heating (which is what you'd get if a few tiles were missing) wouldn't produce the temp changes they're seeing in the data. Only superhot plasma is able to do that, and to get plasma you need a hole.

My own armchair quarterback opinion: they ran over something out there. We've known about the dangers of space junk for decades, and IMO it finally got us. It's also quite possible that the plasma leaked into the wheel well, detonated the tires and threw shrapnel everywhere, and that's what took the wing off.

More as we find it out...