New Scientist: "An unmanned supersonic jet shattered the speed record for plane flight by flying at more than seven times the speed of sound on Saturday.
NASA's X-43A plane flew high above the Pacific for 11 seconds using an engine which expels hot exhausts to propel it forward like a rocket, before gliding for several minutes and plunging into the ocean. It was the first successful demonstration of acceleration by a supersonic combustion ramjet or 'scramjet' engine.
'The scramjet is the holy grail of aeronautics' because it promises the most efficient path from the ground to space, says Joel Sitz, HyperX project manager at the NASA Dryden Flight Research Center in Edwards, California.
Unlike a rocket engine which carries its own oxygen as well as hydrogen fuel, the scramjet engine carries hydrogen fuel only and can scoop oxygen up from the air - making it potentially highly efficient."

Update: Mach 7, 5000 miles per hour.... if only for 12 seconds. You can see BBC video here. (launches realplayer)