Catching up on my Google reading and found this tidbit on Google’s Webmaster Blog. It refers to the strategy of buying text links to give you a better rank in Google.

This confusion lies in the common belief that there are two ways for optimizing the link-based popularity of your website: Either the meritocratic and long-term option of developing natural links or the risky and short-term option of non-earned backlinks via link spamming tactics such as buying links. We’ve always taken a clear stance with respect to manipulating the PageRank algorithm in our Quality Guidelines. Despite these policies, the strategy of participating in link schemes might have previously paid off. But more recently, Google has tremendously refined its link-weighting algorithms. We have more people working on Google’s link-weighting for quality control and to correct issues we find. So nowadays, undermining the PageRank algorithm is likely to result in the loss of the ability of link-selling sites to pass on reputation via links to other sites.

We don’t buy advertising links on sites for fear of this very reason. If the site is a good marketing investment for passing on visitors then a link may be worth purchasing, but if you are buying a link for the purpose of getting better search engine ranking, you might be better off investing the time to find a free link from another site.