VENTUREBEAT — According to new research released Monday by eMarketer, U.S. advertisers will spend an estimated $1.7 billion in ads on social networks in 2010, accounting for 6.7 percent of all online ad spending. The dramatic rise -- with growth of 20 percent this year, accelerating to 24 percent next year -- shows why Google, the biggest player in online advertising, is finally taking the threat from social networks seriously, and Facebook is moving to protect its turf. The gradual economic recovery and the growing relevancy of social media in marketers’ mindshares is credited for the increase in spending...