In a nutshell, online advertising networks will almost certainly survive in one form or another because they continue to offer important efficiencies to advertisers, agencies and media planners.

"Over the last couple of years, the internet has become more fragmented, and advertisers simply don't have the time to talk to every small publisher," says Aaron Kessler, Piper Jaffray senior research analyst. "They handle that issue with a network-based approach. Agencies, too, from an efficiency standpoint, don't want to spend the time to contact hundreds of sites. So I think there's still a lot of value in the networks."

But internet advertisers today want more than simple efficiencies. "I think you are seeing advertisers and brand marketers looking for ways to make better use of their dollars and looking for vertical expertise to help them target and reach specific audiences," says Robert Tas, president and CEO of Sportgenic, a media and technology company focused on connecting marketers to sports enthusiasts. "And I absolutely think that ad networks are going to provide that vehicle."

While smaller sites often rely on networks as their primary sales force, larger sites also need a network relationship to help them monetize unsold inventory. The recent spate of M&A activity around online networks during the past 12 months, in fact, almost certainly reflects the growing understanding of the power and value networks bring to both advertisers and publishers.