eMarketer's latest estimates have U.S. online ad spend at $16.4 billion for the year - 30.8 percent more than 2005's $12.5 billion - driven by Google's online advertising revenues, which are expected to be $4 billion or so.

eMarketer senior analyst David Hallerman writes that impressive growth will continue into next year, with U.S. internet advertising spend expected to reach $19.5 billion - a year-over-year growth of  "only" 18.9 percent due to overall economic weakness in 2007.

Bu in 2008 online ad spend is forecast by eMarketer to increase 22.1 percent increase over 2007, reaching $23.8 billion, in part because of the 2008 election and the 2008 Summer Olympics.