Google no longer honors the nofollow tag! Instead of protecting the  PR/link benefit it used to conserve for non nofollow links, it now  DELETES the PR/link benefit! Stupid move by Google as it again forces  webmasters to look for alternatives to nofollow to protect PR/link  benefit like using javascript when linking to sites we do not wish to  promote!
My SEO advice is do not use rel=”nofollow” on any website if you care about search engine optimization.
To get around this WordPress SEO issue I created a SEO WordPress Theme  that instead of using normal links to link to comment authors URLs it  uses form button links (Google ignores them, no wasted PR/link benefit).
WordPress Comments and rel=nofollow
New  WordPress installations by default now use the rel=”nofollow” attribute  on comment links. If you are not familiar with rel=”nofollow” the major  search engines (Google, Yahoo etc…) issued a new rel attribute  (nofollow) which when used on a text or image link will tell the major  search engines to not consider this as a link that should pass link  benefit (or PageRank in Google’s case).
Link benefit or PageRank  is very important to Google and to a lessor degree Yahoo and Bing search  engine rankings, so adding rel=”nofollow” to a link will mean the  recipient page will NOT gain an advantage in the major search engines.
Text  links and PR are a major part of search engine optimization, without  links (PR) a web site is highly unlikely to do well in Google for  anything but the easiest long tail SERPs. This has led to many  webmasters willingness to resort to dubious (unethical black hat SEO  practices such as blog comment link spamming (I’ve done it in the  distant past).
If you’ve owned a blog that allows comments and to a  lessor degree pings/trackbacks for more than a week or two you’ll  already know what comment SPAM is. If not webmaster add comments to  blogs for a link to their own website(s), that in itself isn’t a  problem, but the comments tend to not reflect the content on the blog  page, usually comments like “great site” or just a bunch of porn, Viagra  or phone sex text links! Comment SPAM started with individuals posting  the comments manually, but now it’s mostly a set of scripts that scan  the Internet for open comment pages to SPAM. This blog has had almost  tens of thousands of SPAM comments, almost all caught by various  WordPress plugins like Akismet, so comment SPAM is a major problem for  bloggers worldwide!
WordPress Comment SPAM Problem
According to Akismet the vast majority of blog comments are SPAM, 92%!!!
My experience of owning blogs agrees with the above, most comments are indeed SPAM   So I fully understand why the WordPress developers have taken this step  due to the plethora of blog comment SPAM currently plaguing the  blogosphere, but it comes at a cost to WordPress users, real commenter’s  no longer get a link back to their site and this is bad for blogging!
The  good news is if you are a WordPress user there are tools (plugins) that  almost stop all comment SPAM (especially automated comments which are  the biggest problem). Like I said above this blog has seen almost 4,000  spammed comments-
Yet only a couple of manually spammed comments got through, so the tools I use work at filtering SPAM.
WordPress Comment SPAM Plugins
Akismet  http://wordpress.org/plugins/akismet/ – Akismet checks your comments  against the Akismet web service to see if they look like spam or not.  You need a WordPress.com API key to use this service. You can review the  spam it catches.
Stallion Responsive Theme package includes built  in comment SPAM blocking plugins that include a comment spam honeypot  that stops the comment from even being added to the database.
The  ones that get through (not many) are handled by Akismet. Akismet filters  the vast majority of SPAMMED comments, but doesn’t immediately delete  them, giving you a chance to recover any comments that are not SPAM (it  happens).
I’m that happy with the SPAM filtering that I’ve removed  the rel=”nofollow” attribute from comments on this blog, it’s a built  in feature to the Stallion Responsive theme. With the odd few that get  through it’s a simple case of manually deleting them. Having the option  to add links within comments you can add your own links and even allow  your trusted commenter’s to benefit SEO wise from their comments.
Removing rel=”nofollow” from comments from a WordPress blog
Quite  easy to remove rel=”nofollow” from a WordPress blog. Either install a  WordPress dofollow plugin or add the following code to your themes  functions.php file:
<?php
 remove_filter('pre_comment_content', 'wp_rel_nofollow', 15);
 ?>The  above is part of Stallion Responsive (and some other nofollow relevant  code), so don’t add the code above if you are a Stallion theme user.
Thank You for David Law 
 
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