ClickBank has been around since 1998 offering businesses and publishers solutions for advertising.
The product for publishers that want to make money from the network is Pay Per Purchase meaning the products that you advertise on your site will pay when your visitors click through and then make a purchase or follow through on a programs requirements.
In all this type of advertising solution for publishers is not the most trackable and often not the most profitable. When your visitor is expected to follow through on a product purchase you move from simply offering advertising placement to becoming a sales agent for their products.
In some situations this can be very lucrative if your site has visitors that need a service or product and you direct them to the sale. The best situation may be niche marketing where you are addressing only a specific topic.
On general content websites the idea of trying to be a sales agent for a variety of products may not have the best results. This would also be true if your site doesn’t match the product you are trying to sell.
There are a variety of Ad companies that offer this type of solution Commission Junction is probably one of their main competitors.
If you are looking for another ad company to fill voids in your sites monetizing plan then take a look at what they offer and try a test run of their product to judge the results based on your sited content.
http://www.clickbank.com/