Many web owners and would-be SEO gurus simply assume that you should only try to get links from “relevant” sites. But there is a problem with the concept of “relevance”.

For instance, if you own a “dog training” site and you link out to your friend’s “craft” site because she makes nice “blankets”, is such a link “relevant” or not?

Or what if you link out to a “news” site because you’ve found an interesting article about the impact of pets on the “health” of hospital patients?

What makes links relevant in such cases (all cases?) is

(a) they come from trusted sources - sites with a bit of history, and
(b) they have link text that relates them to the site they are linked to

But even these factors are open to question. Many web promoters and link builders (including me) have found links from sites with no authority or history showing up in Google backlink reports. For instance, if you post the same article in a number of article sites, it is NOT true that the post from Ezinearticles.com will be the only one to show up. Sometimes the one posted in billy’s-unknown-article-site.com will show up too. There’s no question that the Ezinearticles.com post has a better chance of showing up, but for some reason other obscure sources also make it into your backlink reports.

The conclusion: get links from as many sources as you can, but especially from “authority” sites that have been around for a while. But don’t assume links from new or low PR sites are useless.

For more comments on link relevancy, see this post in Andrew Hansen’s blog - How I Got Shown Up And The Myth Of Irrelevant Links.