Targeting Spam > How a Blogroll can kill your Pagerank
[ Andy Beard] Now there are times you want to sacrifice a little page rank to other sites, especially if they are reciprocating, sharing visitors, or in the case of my blog, I like visitors commenting and joing my “community”. You might also do it in a carefully controlled way from a mininet to one of your own sites.
Some related posts from Technorati and Google.
[B2evolution.net] rel="nofollow" spam prevention - b2evo news blog: 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.
[Sixapart.com] Six Apart - News and Events: Google and a bunch of the blog vendors have introduced a way of anesthesizing URLs in blog comments so that they don't add PageRank. Just put rel="nofollow"
Reflected tags on Technorati: Blog, Nofollow, Targeting Spam