"For about a month and a half I've been paying to advertise my least-popular articles. The result has been that some pages that got a hundred hits a month now get a thousand.
I recently calculated that the links others have given me have over the years been worth from one hundred to one thousand dollars EACH! If you can advertise in such a way as to build repeat visitors and links, then advertising is much more worthwhile." MichaelCrawford
"... it's having a site that's worth someone's time and effort to link to. It's having a site that makes people WANT to link it."
"I think ads discourage linking. Once you do publish ads, test them for a week or two and then remove them from all the nonperforming pages. A page without adsense still gets linked, drives up the pagerank of your site and is a gateway to your other pages. " MichaelCrawford