When I was trying to decide what airline to fly home from KL all the cheapest ones were via Chinese airlines flying like KL->[Chinese city]->Europe. Being a bit of an accident-phobe after too many eps of ACI I always do a bit of research, and while I've forgotten about the details I ended up not choosing any of those, because there seemed to be a lot of attempted hijackings on these flights. Stuff like this: (wiki)
I found lots of other similar cases like this that seemed like semi close calls that I had never even heard of, and they were all on international flights to/from China.
So obviously this is just speculation (since that's what we're here for anyway, right?) but it struck me that there is a decent amount of commercial airline related terrorism type activity going on in China in recent years that I don't think most people are even aware of. MH370 was en route to Beijing and was almost all Chinese passengers, which after all I read makes me think the terrorism theory is somewhat likely at this point given the sudden disappearance, no distress calls, stolen passports, etc.