Yahoo explains how it all works

[janeth]

Yahoo's Priyank Garg Chats with Eric Enge

Eric Enge: Right. So part of what you are pointing at there is that relevance matters a lot. So getting a link from the bottom of a WordPress template that you create and distribute is completely irrelevant.

Priyank Garg: Exactly, that’s the kind of thing that we are trying to do all the time. The irrelevant links at the bottom of a page, which will not be as valuable for a user, don’t add to the quality of the user experience, so we don’t account for those in our ranking. All of those links might still be useful for crawl discovery, but they won’t support the ranking. That’s what we are constantly looking at in algorithms. I can tell you one thing, that over the last few years as we have been building out our search engine and incorporating lots of data, the absolute percentage contribution of links and anchor text to the natural ranking of algorithms or to the importance in our ranking algorithms has gone down somewhat.