If Google doesn’t give any value to those links which are no follow, then why people all over the world make comments in higher PR websites/blogs to get no follow links. Some people give reason that by doing so people visitng those pages may come on that website through that no follow link as they can’t see any difference between do follow link and no follow link. But I am not asking from visitors point of view, I am asking from Google(or in a broad way search engines) point of view. If these no follow links help even a little to take it to top 10 result of search engine result then my question is HOW IT HELPS? Please share your answers and any experiences if you have.
from my experience i can say that No follow link is for driving traffic from that blog to your website. But if you want to build a SEO website i advice you: don’t link them it is a waste of time
NoFollow links will not help you if you want to increase your PR but for SERP it is still useful because SERP is all about your website popularity not DOFOLLOW and NOFOLLOW. Correct me if I am wrong over here…
Short answer - it doesn’t help. People are only commenting in blogs for rank because they are lemmings/muppets/wombles.whatever. They bought into the idea from when the web was pure (before 2004) that each comment link drop counted as a ‘vote’ for their link.
Since the introduction of the rel=“nofollow” attribute for links, most commonly used on CMS/Blogging software, the same lemmings, muppets and wombles keep drinking from the Kool-Aid.
The rel=“nofollow” attribute does not pass any attribution or value (PR) to the destination URL. There’s still some confusion whether Google adds the link to their discovery/crawl process, but that link is still dropped from the algorithm that uses that page’s value for that link.
It does help indirectly provided that the link is relevant enough for real people to follow since a percentage of the people who do follow the nofollow link will create their own backlink to the page that will have value to the search engines.
For me, dofollow link is ranking in search engines and no follow links to drive traffic.
Nofollow links are useful to increase the traffic.But they have not play any role in PR.
As the name suggests, Google (and other reputable robots) will not follow a “nofollow” link, so as far as the search engine is concerned, it makes absolutely no difference. Even if the blogs don’t set “nofollow”, there will be so many links all fighting for the link juice that there will not be enough left to make any difference to anyone.
The benefit to marketing in having links even in “nofollow” sections is that it provides another route for people to get into your site. If there is enough overlap between the content of the site you’re commenting on and your own site, and you present your link well, you are likely to get some traffic as a result of the link. This gets you direct traffic, and may subsequently get you indirect traffic as well - as the person who clicked on your link shares it around to other people. But until it is shared on a “dofollow” page, it will have no impact on search engines.
Why do people do it? Some people would rub snake oil into their mouse if you told them it would get them to #1 in Google. You only need to read this forum for a couple of hours to realise what complete and utter rubbish some people believe about SEO 
As for the google, the nofollow don’t add your backlinks and your pr, but it could bring you the traffic. So the nofollow are also value. And have a import point, though the google ignore the nofollow, the yahoo are accept it.
Here is why nofollow links are okay.
Let’s say I comment on a blog and reference my main site, blackhatbootcamp.com,
in my comment. Then the blog software adds the rel=nofollow attribute to the link.
Next day some rinky-dink crawler, (rinkydinkbot) comes along and crawls that
permalink grabbing all the links. Eventually, rinkydink.com displays, (for some
reason, who knows why it’s a big web), the same link to
blackhatbootcamp.com without the nofollow!
Woot! There’s my link and it more than likely is getting more link juice from
rinkydink.com than it would have from the original blog.
There are tons of upcoming, no-name type of sites that crawl and mirror what they find…
Results 1 - 10 of about 10,620,000,000 for inurl:search.
Ten BILLION just for that query alone!!!
And I love how Google can do nothing about it; it’s the nature of the web.
This is one of the techniques that the SEO insiders use with great success,
while millions of webmaster sit around scratching their butts.
Of course, it does not work every time. It’s more like a machine guy or shot
gun where, if you fire enough, some will hit.
Bompa
Google did something about that long ago. They devalued PR and increased the importance of link relevance so that if the link isn’t between related pages that it is effectively worthless. They also totally discount links from black hat sites so that those links have no value whatsoever. It’s the nature of the web.
Good intentions, bad information presented as stone cold fact as usual. Google haven’t devalued PR, they just stopped showing us what it is, it definitely isn’t devalued since Matt Cutts recently said:
“There is also not a hard limit on our crawl. The best way to think about it is that the number of pages that we crawl is roughly proportional to your PageRank.”
In fact if you spent more time on SEO forums you’d be aware of the debate raging about how important relevance is compared to Site Authority. Links that are from non-related pages can actually be very important Stephen so to say that they’re “effectively worthless” is just plain wrong.
What do you define as a ‘black hat’ site?
Is completely unrelated to what I said and also has nothing whatever to do with SEO.
Oh really?
When I look at the back links of the top ten in ANY niche, I see some related
sites and some non related sites.
What is Google’s advice on getting links?
Put something of interest that others want to link to.
So, if you create a site with humorous pics or stories and others link to you, how then
do you control the relatedness that you say in necessary?
Bompa
Again, I see where you’re coming from but you just keep doing flybyes on the pertinent issues. Pagerank hasn’t been devalued, if it had it wouldn’t influence the crawl budget and Google wouldn’t have felt the need to prevent people ‘siloing’ it would they.
You also completely ignored the bit where I shot down your theory about the importance of links from non context related sites, you have nothing to say about that?
I’m still waiting for your definition of a ‘black hat’ site, but maybe I should just add it to the long list of things I’ve been waiting for answers from you about.
it’s useless some webmaster will not add a dofollow tag on their outbound links for the simple reason that they don’t want to pass link juice on another site
They will link to you BECAUSE they decide that your page is related to theirs. If they didn’t think it was relevant then they wouldn’t link to you. Natural linking is always relevant. It is where YOU try to generate links yourself that you can end up with unrelated ones.
Nofollow backlinks are still effective when increasing your SERP ranking, they just simply don’t pass on any link juice, which is what gives your website a pagerank, but ranking highly in the SERPs generally does give you a higher pagerank, so nofollow backlinks can still non-directly give you a higher pagerank. 
There are two reasons why you should not give up nofollow links.
First they can bring you traffic. Then they can make your links appear more natural than with only do follow ones.
Still waiting for your definition of a ‘black hat’ site so we can ascertain the accuracy of the above statement. Been waiting for quite a while now.
So the only reason someone would link to you is if your content was relevant to theirs and natural linking is “always relevant.” is it? Do you want to have a rethink on that one and get back to us?
Maybe while your’e doing that you could give us your opinion on the debate raging in the SEO world on why links from non-context related (i.e not relevant) authority sites can be worth more than relevant links from less authoratitive sites?