peterupton asked: I have heard figures of 50 cents (per John Batelle, the Google search authority) to $1.43 (per Fathom Online, an online trends tracking company).

M S asked: This must be tracked and published somewhere (preferably somewhere with free public access). I would like to look at the trends over the last 20 years or more as well as recent data over the last 5 years or so. You do not need to compile this, but just point [...]