EMARKETER — Social network advertising is getting renewed attention in 2010. The US’s gradual economic recovery, combined with marketers’ incessant focus on reaching consumers in social media, has led companies to make big increases in social network ad spending in the first half of 2010. eMarketer estimates US advertisers will spend $1.68 billion on social networking sites this year, a more than 20% increase over 2009. Spending will rise even further by 2011 to more than $2 billion...