How does search engines like Google handle rel=”nofollow” links?

nofollow is an HTML attribute value used to instruct some search engines like Google that a hyperlink  should not influence the link target’s ranking in the search engine’s index. Also most of the search engines does not follow the links marked rel=”nofollow”.
nofollow improved quality of search engine results by preventing spamdexing.The concept for the specification of the attribute value nofollow  was designed by Google.

Example of rel=”nofollow” is given below
<a href=”http://www.abcdxyz.com/” rel=”nofollow”>This is a nofollow link</a>

Quality back links are one of the most important factors for SEO success and is hard to get.Do a search for any website for it’s back-links,you will find many or majority of the links will have nofollow attribute.

So how does different search engines handles rel=”nofollow” attribute?

• Google states that their engine takes “nofollow” literally and ‘In general, we don’t follow them.’Google does not transfer PageRank or anchor text across nofollow links. Google does not index the linked-to page, unless it was in Google’s index already for other reasons like if other sites link to them without using nofollow, or if the URLs are submitted to Google in a Sitemap.
• Search engine Yahoo! follows the rel=”nofollow” link but excludes it from their ranking calculation.
• Bing respects the rel=”nofollow”
• Ask.com search engine does not consider the rel=”nofollow” attribute.