The latest "Dawn" release will apply a rel="nofollow" by default to all comment/trackback links posted on a blog. Since I get all sorts of questions about that all the time, here is a quick explanation...
The purpose of rel="nofollow" is to tell Google (and most other major seach engines) this "I don't know who posted this link, I cannot guarantee it is relevant, I am not endorsing this link". The result is that this link will have no contribution in raising the refered site's pagerank and placement in the list of results.
The indirect purpose of having that by default in b2evolution is to tell spammers this: "Do not bother searching for b2evolution powered sites on Google in order to post spam in them, because spam on those sites will provide *no* contribution in raising your site's pagerank...".
Before "Dawn" it was exactly the opposite. b2evo was like a honeypot for comment spammers.
In a similar manner, "Dawn" won't display any referers publicly any longer. This again is to tell spammers this "Do not bother referer spamming b2evolution blogs, because your referers won't even appear anywhere to be seen".
Now, the question many people raise is this: "When someone posts a legitimate comment, I want to endorse the link to his site and I want Google to give that site a little love on my behalf...". Right. We understand that. The plan is to have a checkbox in the backoffice to remove rel="nofollow" from comments you have approved, but *only* those that you have approved. Again we don't want spammers to get through it. Also, when a comment is suspect, sth like "Nice site." and an URL to a page that is "Under Construction" (i-e waiting to be used...) we encourage everyone *not to* endorse the URL, even if you might want to keep the comment...
Next question is "when?". The Answer is "Phoenix", a few weeks, something like that... unless someone comes uo with a hack earlier.
PS: no need to send links to all those sites arguing about rel="nospam". 8 out of 10 of these arguments are irrelevant, and the remaining ones just can't outweight the spam stress we all get by not being firm on blocking it.