It looks like Google is soon to get some serious competition in the advertising space, as the Wall Street Journal is reporting that Amazon has something cooking. Called "Amazon Sponsored Links", Amazon's advertising solution would take Google's AdWords head-on, where relevant ads would be displayed based on the context of a search.
Amazon's target: Google AdWords
Google's advertising platforms make up a huge portion of its overall revenue, and Amazon happens to contribute a fair bit to that. You'd be hard-pressed to search for a product on Google and not see an Amazon link up top, and further, Amazon.com has been integrating Google AdSense in parts for a while. It goes without saying that Google would notice Amazon's AdWords departure.
With Amazon's competitive target being AdWords, it seems likely that a service to compete against Google AdSense would also come along in the future. That would allow website publishers the ability to integrate Amazon advertising inside of their websites, and really push into Google's domain.
It's also being noted that the company is creating a tool that will allow advertising agencies to purchase ads in bulk, on behalf of all of their clients. This shows just how serious Amazon is about its advertising venture, and just how serious Google will be treating it as a real threat. To Google's advantage, it has a 14-year head start, but I'm pretty sure it'd rather not have any competition come to it in the form of a behemoth like Amazon.