Here's another theory, very technical but if true the plane will be very hard to find. It also explains why the transmission was lost. If the plane hit the water nose first it probably would've gone down without any visible debris on the surface. Interesting read and plausible. If we're forced to accept that all have perished this would offer some comfort that none of those on board were conscious of their plight and didn't die in terror.
http://mh370lost.tumblr.com/?og=1
Summary: It's plausible that a fuselage section near the SATCOM antenna adapter failed, disabling satellite based - GPS, ACARS, and ADS-B/C - communications, and leading to a slow decompression that left all occupants unconscious. If such decompression left the aircraft intact, then the autopilot would have flown the planned route or otherwise maintained its heading/altitude until fuel exhaustion.
A slow decompression (e.g. from a golfball-sized hole) would have gradually impaired and confused the pilots before cabin altitude (pressure) warnings sounded.
Chain of events:
Likely fuselage failure near SATCOM antenna adapter, disabling some or all of GPS, ACARS, ADS-B, and ADS-C antennas and systems. Thus, only primary radars would detect the plane. Primary radar range is usually less than 100nm, and is generally ineffective at high altitudes.
If the decompression was slow enough, it's possible the pilots did not realize to put on oxygen masks until it was too late. (See Helios 522)
Also explains why another Pilot thirty minutes ahead heard "mumbling" from MH370 pilots. (VHF comms would be unaffected by SATCOM equipment failure.)
With incapacitated pilots, the 777 could continue to fly on Autopilot - programmed to maintain cruise altitude and follow the programmed route. Using the Inertial Reference System (gyroscope based), the plane could navigate without needing GPS.
Conclusion:
This was likely not an "explosive decompression" or "inflight disintegration." This was likely a slow decompression that gradually deprived all crew/passengers of oxygen, leaving the autopilot to continue along the route autonomously.
The aircraft may be at the floor of the East China Sea, Sea of Japan, or the Pacific Ocean thousands of miles northeast from the current search zone.