I'm going to assume that because you clicked on this, you've already been following all the news about Flight 370, so I won't bother with any introduction. I'm simply starting this because I want to talk about it more than I can do on TB's Gawker threads.
So. We have to start somewhere. And that somewhere, is that the plane is somewhere. The simplest explanation is that it's at the bottom of the Indian Ocean. And here we run into the problem that every single explanation has problems, some of them fatal. My problem with the "it just fell into the ocean" idea is that, going on two weeks, nothing has been found. No debris of any sort, anywhere. Zilch. While the area it could have gone down in is huge, after 11 days, the debris field would have spread over an awfully large area as well. So this seems increasingly unlikely with every passing day.
So let's back up a moment and consider the one piece of solid evidence we have (a collection of related clues, if you want to be exact), and that is that the plane was carefully and deliberately diverted from its intended flight path by someone with professional training in how a 777 functions. That eliminates the viral "there was a fire on board" theory, because the plane was diverted by reprogramming the navigational computer—not something a pilot would bother doing if the plane were on fire and he was just looking for the closest place to land.
Pilot suicide has been advanced as another "most likely" explanation, but this too has problems. First, we're back to where it went down and the lack of debris. Also, there has been absolutely zero evidence to come forward suggesting either pilot had any personal issues pointing toward suicide—in fact, the co-pilot was about to get married. Possibly one of the other flight crew was responsible, but that runs up against the problem that only an experienced pilot would have been able to disable all the communications systems.
So if the plane didn't go down in the ocean, where is it? It almost certainly couldn't have crashed on land because someone would have noticed the fire and smoke that would have resulted. Possibly unreliable data suggests it flew for another 7-8 hours after the last contact. The southern route ends in the middle of nowhere. There's no reason to go that direction absent a suicide attempt, and as to that, see above. The northern route takes it over multiple countries with military radar systems that should have detected it.
Here, I think the seemingly preposterous "flew behind another plane" idea actually has some legs, because it fits with the careful redirection of the plane and its behavior after communications were cut off. It also helps explain how it could have flown north seemingly undetected. The Thai military revealed this afternoon that they think they might have detected the plane in the early stages, but did nothing because it "didn't seem like a threat."
That attitude, in my mind, is likely how it could have managed to get so far without being spotted. As a vet myself, I can tell you that, in peacetime, the attitude of most military personnel faced with these kinds of situations is to take the path of least resistance. No apparent threat? It's nothing serious, let it be. As just one example, the Japanese planes that attacked Pearl Harbor were actually picked on radar on their way in, but the American personnel that spotted them thought they were a flight of B-17s from the mainland, and anyway, who would be attacking us? It can't be anything dangerous. I can easily see the same thing going on as the plane made its way north.
But, then what? If you trace the flight path of the Singapore Airlines flight it was supposedly following, it traverses much of northern India and Pakistan. At the limits of its fuel range, there are places it could have turned off and landed. Except. There is no airport, simply none along this flight path, where a 777 could have come down without someone noticing—especially not once news of the plane's disappearance spread. That, as much as anything in this saga, is just impossible.
So where did it land, assuming it did? The 777 is not designed to land on an improvised runway, but that doesn't mean it is not capable of doing it. If you look at Google Earth in Central Asia, there are quite a few flat, desolate areas—dry lakes, salt pans, and the like—where you could conceivably build a 7,000 foot runway without anyone noticing, at least if it was done recently. Building a runway isn't that complicated if you've got a few bulldozers to do it with.
A few years ago, my father and I took a fishing trip to northern Canada, and we flew into an island in the middle of a very large lake, where the owner of the place had built an entire fishing resort by flying things in on a big float plane—including a bulldozer, which they flew in, piece by piece, reassembled, then cleared out a runway for the charter planes to come in. Granted, we flew in on a small commuter plane, not a 777, but the terrain was quite a bit more rugged than a deserted flood plain in a the Taklamakan Desert. More difficult, to be sure, but the same approach.
So, here is my pet theory on what might have happened.
Somehow or another, whether through threats, bribes, or some other inducement, some group, terrorist or otherwise, is able to engage the cooperation of the flight crew to redirect the plane. They shut down all the communications gear, turn west, depressurize the plane to knock out the passengers, and take the plane up to 45,000 feet until they're all dead. They come up behind the SIA flight and follow it up across India. At some point when they get to northern India or Pakistan, they turn off and land at a point where other members of the group have constructed a runway.
There, the plane is concealed from satellite surveillance by draping it strategically with camouflage netting, painted canvas, and the like. This is easier to do than you might think—the Soviets trained their allies across the Third World in ways of concealing things from U.S. spy satellites, and that knowledge has surely trickled down. The same thing goes for the runway—you could disguise the otherwise giveaway straight-line shape of it without a lot of effort.
Once concealed, the dead bodies are removed and buried in a mass grave, perhaps using the bulldozers that are already there and the earth that has already been displaced for the runway. The plane is then loaded up with whatever explosive material has been pulled together, in preparation for some dramatic attack.
The problem with this theory, of course, is that it's patently ridiculous. It's a James Bond movie, not reality. It's so overly contrived it that it's extremely difficult to imagine anyone actually plotting it out. Even assuming some terrorist group wanted to steal a plane and turn it into a flying bomb, why this plane? Surely there would be far simpler means of doing this.
tl;dr, basically, I'm out of ideas.