I dug lately this particular forum and similar places on other websites and I noted the industry of contextual advertising is blooming, meaning there are a many small players now in the market, many of them cloning the AdWords + AdSense duo. How do you foresee their evolution? I personally believe most of them will fail sooner or later to achieve the "crtical mass" required to keep such a system living, however if they do and they also improve the concepts we're used to they could cross the barrier of 0,10% market share As an advertiser would you consider them? Personally, I would provided the price is competitve and if I have access to tools that will enable me to properly track the audience. However, I'd monitor the advertising campaign in a strictly manner.
If you advertise something very general it worths using a small player because the CPC is usually very smaller. But when you need really targeted visitors (eg. for an eshop) most of these companies don't have the technology to help you....
I feel that it's just like anything else when it comes to business. The more that set up, the more competition there will be making it harder to compete against the bigger players in the market. This will mean that there will always be new contextual ad networks starting, but at the same time there will also be some closing.