We go to Google, Yahoo and Bing to shop. We go to social media sites to network and wise off. So here's the 500-lb. gorilla question. Why would you ever pay to advertise to people who by definition are neither shopping nor primed to purchase? Most of them are going to just shut out the message. Or, if they notice the message, it will make the shallowest of impressions. The message blends into the background noise of the mind, becoming invisible in plain sight.

That conundrum still looms large as LinkedIn sets the advertising world abuzz by remaking itself as a marketing venue. In June the company added new targeting options for advertisers. Ads are custom-served to you based on characteristics cataloged through data capture. LinkedIn further sweetened the pot recently with new and improved company pages. They used to be masses of gray text. Now you can jazz them up with brand imagery.

Is LinkedIn copying Facebook? Oh heavens no, company leaders insist. But I think they doth protest too much. If it looks like a duck, walks like a duck and quacks like a duck . . . it's Facebook. The question for you the advertiser: How well will it work? Compared to Facebook advertising, I think LinkedIn advertising could get better results. My reasoning: LinkedIn is a networking site for ambitious, highly educated, serious professionals. All about business. A virtual office. So you expect ads. Maybe even welcome them.

But Facebook? An amusing digital playground. All about wall-to-wall goofing off. Do you really take serious anything you read there? And how does that taint your perception of the ads?

While the developments at LinkedIn are intriguing, I still doubt we'd ever recommend it as a primary advertising buy. It does increasingly look like a peripheral base you should cover. And yes we now rank it ahead of Facebook. Just don't put all your eggs there - or at any social media site. Instead center your digital marketing campaign on the websites people visit to shop. Target the visitors who are there to consume advertising, their eyes and ears wide open.