I enjoyed watching him (periodically) anchor in place of Tom Brokaw, and watching his segments on MSNBC. I think he genuinely enjoyed being in Iraq on this assignment. He will be missed.
Asked my wife what might have caused this, and she indicated that she's seen this before in people who sit in planes for long periods of time without much movement, causing a clot to develop in the lung area. I wonder if his confinement in military vehicles for the last few weeks were a key factor?