US advertisers will spend $24.9 billion on online advertising this year, eMarketer predicts (via MarketingCharts). That's $1 billion less than its previous estimate, issued in March, but still represents double-digit year-over-year growth of 17.4 percent, it said.

Online ad spend will slow a bit in 2009, growing less than 15 percent YOY, before beginning a significant rebound starting in 2010 through 2012.

The additional dollars of online ad spend are being taken away from budgets for traditional media, such as TV, according to eMarketer.

"Even as the potent mix of a misfiring economy and consumers' changing media habits shave advertising dollars from traditional venues, such as newspapers and television, internet ad spending will continue to grow rapidly," David Hallerman, eMarketer senior analyst, is quoted as saying.

Though the firm estimates that TV ad spend will grow 7.1 percent this year, reaching $72.6 billion, it projects that in 2009 TV ad spend will decrease 2.6 percent, then grow just 1 percent or 2 percent the subsequent couple of years.

Newspaper US ad spend is forecast by Borrell Associates (March 2008) to fall to $45 billion in 2012 from $50.8 billion in 2007.