In 2007, ad spending on US social networking sites is expected to spike to $865 mln from $350 mln in 2006, according to eMarketer. By 2010, eMarketer estimates, spending will hit $2.15 bln. Worldwide social network ad spending will reach $1.1 bln in 2007, up from $445 mln in 2006. By 2010, spending is expected to rise to $2.8 bln.