As I write (at 9:30pm EST in the US, 0230 March 8 GMT), things look bad for Malaysian Airlines flight 370 from Kuala Lumpur to Beijing, but nothing is known for sure.
The most illuminating information I have seen so far is this log from Flight Aware. It shows that the airplane had leveled off at 35,000 feet -- and then suddenly was not transmitting any more information about its location, speed, altitude, or rate of climb or descent.
Clik here to view.

It is hard to imagine a systemwide failure of the transponder and other reporting equipment that could have made the plane stop reporting any information and yet still be flying along safely. (And in that case, it would presumably have tried to land somewhere along the Malay peninsula.)
The main insight I have to add for now is: Whatever happened, it is unlikely to reflect chronic shoddiness with Malaysian Airlines, which in my experience is a good, competent, and modern airline (I have flown MAS many times, including on this route), nor with the Boeing 777, a good and well-experienced airplane. Beyond that, we await further news with best wishes for all involved.
Image may be NSFW.Clik here to view.

Image may be NSFW.
Clik here to view.

Image may be NSFW.
Clik here to view.

Image may be NSFW.
Clik here to view.

Image may be NSFW.
Clik here to view.

Clik here to view.

Clik here to view.
