A proxy for the trend toward the intangible economy

I ran into this piece of information in a recent Economist story on oil prices -- Economics focus: Shock treatment:

Rich countries use less than half as much oil as they did in 1970 for each inflation-adjusted dollar of GDP. So although prices in real terms have returned to levels last seen in the 1970s, their impact is not as powerful when set against the diminished economic importance of oil (see charts).

That is a strong measure of the extent to which the economy is becoming, as Alan Greenspan used to say, "weightless."