A rel=”nofollow” link is used when you do not want to spiders to go to the website your linking to. So you would use this for blog comments, link exchanges, paid links, etc. All 3 search engines say they do not follow the link at all. They advise you to use nofollow for anytime you do not want to have the spiders crawl the website your linking.

However, Its been proven many times that Google and Yahoo still give weight to websites that are linked with the nofollow. Its not as much a link without the nofollow, but it still helps.

I will be doing a test soon to test this.