The fate of the Mars Climate Orbiter is rather amusing.
The metric/imperial mix-up that destroyed the craft was caused by a software error back on Earth. The thrusters on the spacecraft, which were intended to control its rate of rotation, were controlled by a computer that underestimated the effect of the thrusters by a factor of 4.45. This is the ratio between a pound force - the standard unit of force in the imperial system - and a newton, the standard unit in the metric system. The software was working in pounds force, while the spacecraft expected figures in newtons; 1 pound force equals approximately 4.45 newtons.
The software had been adapted from use on the earlier Mars Climate Orbiter, and was not adequately tested before launch. The navigation data provided by this software was also not cross-checked while in flight. The Mars Climate Orbiter thus drifted off course during its voyage and entered a much lower orbit than planned, and was destroyed by atmospheric friction.