Internet advertising revenues in the U.S. hit $5.9 billion for Q1 2010, representing a 7.5 percent increase over the same period in 2009, according to numbers released moments ago by the Interactive Advertising Bureau in tandem with PricewaterhouseCoopers. This marks the highest first-quarter revenue level ever for the industry. Nevertheless, revenues came in much lower than the fourth quarter of 2009, when online advertising revenues in the U.S.