Long seen as the repository of less desirable, remnant inventory, the traditional definition of ad networks is quickly evolving. The rapid consolidation within the ad network industry has left few independent, stand-alone networks. Likewise, specialized ad networks, focused on behavioral targeting or vertical content, are also becoming increasingly scarce.

The reach of the larger networks is now astounding -- comScore estimates that AOL's Platform A now reaches more than 90 percent of the U.S. internet population. But reach only hints at the potential value of an ad network to a marketer.

With consolidation comes a change in the revenue structure of these businesses, as bargains become more challenging for ad buyers to find. However, as ad networks increasingly move upstream, representing more and more premium inventory, there are still common misconceptions about the strategic value of buying media through a network.

Let's take a look at some of the most common myths about ad networks and examine the realities.