martinibuster - 11:35 pm on Jan 11, 2012 (gmt 0)
The nofollow tag prevents PageRank and anchor text from being passed on to the receiving site, but it does not stop trust and relevancy...
Trust is not a signal that is passed through a link to a website. There is no signal called Trust. That's not what trust is. There are a lot of SEO Myths associated with trust and to expand further, I want to include the so called Trust Rank that is sometimes spoken of in the context of Google's algorithm. TrustRank is actually associated with Yahoo [ilpubs.stanford.edu]. Here is what Matt Cutts said [seroundtable.com]:
Trust is sort of a catch-all term that we use. So PageRank is the most well known type of trust. It's looking at links and how important those links are. So if you have a lot of very high quality links, then you tend to earn a lot of trust with Google.
In Matt's scenario, a website can earn trust by receiving gobs of PageRank. But if it has a nofollow attached to it then no PageRank is passed and as a consequence the web page does not earn trust. In other words, the web page has to qualify for the Not-Spam Bucket and one of the ways to qualify is by getting gobs of PageRank. Trust itself is not a signal that is passed on by links.
Similarly, relevancy is not a signal unto itself that is passed on to the linked site. Relevancy is an aspect of a link that helps determine how much PageRank is passed on to a site. A link with low relevance passes less PageRank. A link with higher relevance passes more PageRank. If there is a no-follow attached to the link then no PageRank flows, so relevance doesn't matter.
In the context of links, relevance only modifies the amount of PageRank that flows. That's all. It's not a signal that is passed on through a link.