Reciprocal links have long been both the bane and salvation of the individual SEO working away on his/her own small website. Recip links get slammed in the forums and touted by others. Why is there no consensus? Why is this issue still around nearly 10 years after it first became and Internet marketing tactic?

The answer is that some reciprocal links can and do help. The reasons are very simple - search engines are seeking authoritative, on-topic links and just because they recognize that CNN links to NASA and NASA links to CNN doesn't mean that the link should be devalued. This applies across the spectrum of the entire world wide web. Topical communities, which are the basis for local link popularity (first used by Teoma and now adopted by all of the major SEs), are based on reciprocal, 3-way and 4-way links. Let's use the search engine optimization industry as an example:

SEW links to Threadwatch links to SEOmoz links to SEW links to SERoundtable links to Cre8asite links to SEOChat links to SEOmoz links Threadwatch links to SEW, etc.... ad nauesum.

Are these sites the subject of penalization in the SERPs? No. They all rank in the top 10 for thousands of related search terms (well, for SEOmoz - hundreds, at least). Reciprocal and interlinking is what creates web communities focused on the same topical matter. But, these reicprocal links share a pattern - they don't all link to one another from off-topic, purely external link pages. They have related content describing one another or pointing to valuable information directly on the topic of the page.

What we can say is that linking to a Slashdot entry that mentions your website probably won't hurt you by devaluing the link (due to reciprocity), but having all your links from other sites' off-topic, reciprocal link collections pages may not help nearly as much.