Frequent flyer miles currently in circulation exceed $500 billion in value, making them the second biggest world "currency" after the US dollar. And at their current rate of growth, flyer miles "could overtake the dollar within two years". Where will we spend them? According to this related article in the Economist, "US Airways has launched a deal where, for a mere 10m miles, you can buy a seat on the first private spacecraft to take passengers into space, scheduled for 2004."