Online ad spending in the US is growing more rapidly than any other advertising medium, is reaching new heights seemingly with every passing quarter, and has been projected to see double-digit growth again this year. In fact, the IAB estimates that online ad spending has grown at a compound annual rate of about 20% over the past 10 years. But to what extent is this meteoric rise simply a result of marketers chasing a growing online population? Removing inflation from the equation, is each individual internet user worth more to advertisers today than a decade ago? This article pulls together data from various sources to measure the real growth in spending per online user from 2000 through 2012. Read the rest at MarketingCharts.