This network can be nice for webmasters who would like some rather affordable, quick and massive exposure for their ads. When you compare the price tags with those of PPC, you will find most of them very inexpensive but they could be weaker when it comes to building traffic for websites in some cases. The ads in sidebars are almost always very weak, and they may not be helpful that much.
Just have a look at most websites which sell advertising spaces, you will find the top positions bought quickly by advertisers as they will be seen by most visitors, increasing chances to have clicks and page views and they are expensive too. The real problem is that you will buy a monthly ad placement, there could be tens of thousands of impressions but no guarantees for clicks and targeted traffic.