It's the number one question of our client who are considering a PPC program with Google Adwords, "If I'm already ranking well in the organic listings, why should I pay for ads on Google?"
I usually offer up a few reasons including:
We've had two occasions at Interactive Strategies when clients went cold turkey and turned off their Google Adwords and other PPC programs. The results were surprising -- not only did our clients' paid traffic drop, but so did their organic traffic.
Finally, this article in today's New York Times offers some interesting proof of this interesting phenomenon and supports our theory that a PPC program can actually boost the impact of SEO.
While the author speculates that Google may boost organic rankings based on paid listings, we're rather confident the reason is based in a fundamental marketing principal: the more impressions you make, the more likely someone is to respond to your ad. So consider the PPC ad the first impression and the organic ranking the second impression.
If our theory holds true, it means that every dollar spent on a PPC program is even more valuable then we originally thought.