Comment on Rel Nofollow by SEO Dave.
So what happens when you have a page with “ten PageRank points” and ten outgoing links, and five of those links are nofollowed? Let’s leave aside the decay factor to focus on the core part of the question. Originally, the five links without nofollow would have flowed two points of PageRank each (in essence, the nofollowed links didn’t count toward the denominator when dividing PageRank by the outdegree of the page). More than a year ago, Google changed how the PageRank flows so that the five links without nofollow would flow one point of PageRank each.
So it is not used by the 5 dofollow links, it’s gone, kaput, deleted :-) In the examples used 50% of the pages link benefit is lost for no gain!
Years ago it used to be the nofollow links as far as Google was concerned didn’t exist, the anchor text was supposed to be ignored and the link benefit used by the dofollow links. Currently Google is supposed to ignore the anchor text of nofollow links (there’s been edge cases where it’s counted) and delete the link benefit. This means there’s nothing but SEO negatives to using nofollow, not only does it delete the link benefit you also don’t get the anchor text benefit or the SEO benefit of linking to related niched pages!
On my sites I never use nofollow, you will note the link to Matt Cutts blog post is body text (Stallion feature, you can stop WordPress converting URLs to clickable links), either add a non-clickable link, cloak the link or pass link benefit (dofofollow). There’s a Stallion feature that can automatically convert your nofollow links to cloaked links (I have about 90 WordPress blogs, probably 100,000+ comments, had to find an automated solution :-)), so if you have loads of nofollow links Stallion can convert them on the fly (the database isn’t edited, switch themes they revert back to nofollow) until you find the time to edit them.
There’s a Stallion feature not to nofollow clickable comment links (WordPress by default adds nofollow) like this one SEO Tutorial so if you want to use links within your comments without adding nofollow… Does open you up to link SPAMMERS but I have my sites set to moderate any comments with even 1 link and only use this feature on sites I’ll add clickable links on (only a few).
The SEO impact of nofollow can be irrelevant or catastrophic, depends on your setup. For example if you’ve used WordPress SEO Plugins like Yoast WordPress SEO and have set the plugin to nofollow all archive links that’s a LOT of nofollow links, it wouldn’t be difficult to use Yoast WordPress SEO and similar plugins to have more nofollow links than dofollow which would be catastrophic! In comparison a page with 99 dofollow links and 1 nofollow link wastes just 1% of that pages link benefit, not a big deal.
If you are adding nofollow links to relevant resources (like Wikipedia) believing it has a positive SEO impact you are wrong. All you are doing is deleting your hard earned link benefit.
I always aim for zero nofollow links, don’t see the point in deleting link benefit.
On forums I don’t like forum software (have a few dead forums), the moderation is rubbish, gaining users is hard, having WordPress sites with open comments is both easy to manage and easy for users to comment and with Stallion SEO Super Comments from an SEO perspective this comment will be indexed in it’s own right and potentially gain relevant SERPs on nofollow etc…