We get a LOT of traffic from Google's organic SERPS daily (over 300,000 visitors, actually), but we still use PPC to supplement that. In our case, the traffic that we get from organic is very different from what we get from PPC.
Our organic traffic is long-tail towards individual forum threads on the site. People come in from the serps, read the page, and then move on. It accounts for the majority of our page impressions, but people who are doing Google searches are currently in research-mode, and are not in the market to start joining a community.
We therefore rely on PPC to help sustain new blood into our community. We have found that people who come into our forum listing pages spend more time on the site and are more likely to register and post. However, because these are navigational pages and don't contain actual content, Google doesn't send any traffic to these pages. Therefore, we need to rely on PPC to send traffic to the pages that convert the highest for us.
cscgal
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