Recently, I got a piece of blogspam emploring me to turn off "no follow" on my comment links in order to increase my blog's readership. The "rel='nofollow'" attribute on a link (for those who don't know) means "I do not endorse this link - it was added by a user of the site, and may be spammy in nature", and is used by search engines (Google in particular) to mean that it should not contribute to the linked page's pagerank.
My first reaction was revulsion that spammers would use such a down-right dirty tactic. But then I realised that if spammers are doing this, it means that nofollow is working - it's getting harder to get non-nofollow links to your site via spam, and therefore harder to fraudulently increase your pagerank. This is a very good thing for bloggers because if spamming blogs is no longer effective, it will stop. So (in order to counteract any damage that this "disable nofollow" spam might do, I encourage bloggers and operators of other sites where users can add links to ensure that the "rel='nofollow'" attribute is placed on all links that you haven't personally checked and endorsed. It has no effect either way on your readership (only producing quality content that people want to read can do that) but it makes the efforts of spammers useless. Also beware of anyone coming out of the blue and wanting you to link to their site (even if they're offering reciprocal linking) - chances are they're SEO spammers.