Will Facebook, Twitter, and other social networking sites put Google AdSense out of business? It’s not such a far-fetched notion, if the results from a new online retailing survey bear out:

The study involved 117 online retailers polled between Feb. 18 and April 1. The companies, which [study sponsor] Shop.org didn’t name, reported scaling back hiring and their increasingly expensive search marketing programs, which include paying for top billing in the results consumers see for their Web searches. Online merchants whose business is beating expectations will likely fuel much of the e-commerce investments in the coming months, the survey found.

“Online retailers want… to be more efficient in getting a bigger bang for the buck,” said Scott Silverman, executive director of Shop.org.

Developing social media marketing requires some investment in personnel, he said, but many merchants see big opportunities to spread a positive message about their brand for relatively low cost.

In other words, why pay Google an inflated price for prime keyword placement atop a long list of hit-or-miss search results, when you can get low/no-cost bloggers/tweeters to spread goodwill directly to a focused audience?

Ultimately, it’s about hitting the same channels as your potential customers, and current search engine marketing (SEM) does an imprecise job of that. Pimping amongst Facebook pokes isn’t necessarily the most effective method either — the previously-cited “seat at someone else’s table” sales pitch — but because it’s so cheap, there’s less risk involved.