Online ad spending in the US is growing more rapidly than any other advertising medium, is reaching new peaks 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 20.3% in the past 10 years. But to what extent is this meteoric rise attributable to growth in the online user population, as well as inflation? This article pulls together data from various sources to measure the real growth in spending per online user from 2000 to 2011. Read the rest at MarketingCharts.