By some accounts, there are over 150 ad networks or exchanges currently operating in the U.S., which begs the question of sustainability in an increasingly crowded market. According to Wiggins, portals and large content sites will continue to invest in ad networks, as the third-party services provide much-needed improvements in content monetization. "Meanwhile, consolidation/shakeout will continue in commoditized networks," he said. "For example, some performance-based networks may be marginalized by ad exchanges." Still, Wiggins said that networks and exchanges that offered competitive tech or other advantages would continue to attract investor interest.

On the other hand, investments in mobile marketing tech and services, which Petsky Prunier also grouped within the Interactive Advertising sector, have slowed significantly. Holding companies and VC firms funneled just $80 million into mobile marketing firms in the first half of 2008, down from $291 million last year.

"(Mobile) was the largest recipient just two years ago," Wiggins said. "As investors were perhaps hoping that 'if you build it, they will come.' But the infrastructure hasn't facilitated its use." And Wiggins said that even the new 3G iPhone wouldn't spark increased interest (or investments) from financiers in the short term.