A new report by eMarketer estimates that by year-end, digital advertising will hit $37.31 billion. But that was only half the story; the interesting observation made by eMarketer is that Google is on track to topple Facebook as the leading platform for display advertising. The estimated passing is more of a return to the top for Google. Back in 2010, the search giant had a slight edge over Facebook with 12.1% of the display ads market. That all changed in 2011 when Facebook rocketed pass Google with 14.1% of the display ads market. eMarketer estimates that the improved market share for Google will translate into $2.31 billion in revenue for US display ads; Facebook is tipped to earn $2.16 billion.