I'm not so sure that the pilot didn't highjack the plane to blackmail the Malaysian government, which he opposed. Five days before the flight, an opposition leader he supported was jailed for 5 years. He reported wore a shirt saying "Democracy is dead".
The problem with this theory, though, is that U.S. spy satellites would have found the plane, unless there were co-conspirators and it ended up in a hangar. That would explain why there were no pings from the black box.
On the other hand, there apparently is a lot of junk floating around in the Indian Ocean, and wreckage might be found. The Aussie chap, Angus Houston, said as much in his press conference earlier today.