A slashdot thread last week reported how all too often mathematical conversions can go wrong. In this case, Spaceship One thought they were 100km above the ground to claim the X-Prize when they weren't. Strikes a similar chord to the Apollo 13 square peg to fit round hole problem. Indeed, one of NASA's less-than-stellar conversion problems really did occur because half a Mars orbiter was constructed in inches and the other in centimeters. And indeed, one guy has found a couple of dozen metre to inch conversions on the web with different results.
I wonder how you can take advantage of poor conversions rather than suffer their consequences. One story told the tale of a student who wanted to use Euros in London the first day they were issued. Due to a currency exchange flaw at one store, he always got given the wrong change in pounds sterling and made money with every transaction. Wonder what else is out there?