I think Phil Ringnalda is right about nofollow:
It only actually stops you from getting spammed when the ocean starts boiling, after we've forced every single person with weblog comments to implement it, and driven the unbelievers off the web. Until then, the spammers and the search engines are going to keep working you from both ends, but the search engines want to make sure they don't catch anything from you.
Google doesn't care about us webloggers; what Google cares about is our links. Links are what PageRank feeds on, and PageRank is what Google really cares about.
Google didn't decide to do something about it because our bandwidth is being stolen and our pages littered with spam. No, Google introduced nofollow because the spammers were warping PageRank. It isn't a solution to our problem; it's a solution to Google's problem.
As Phil and others have argued, this isn't going to stop the spammers; they're just going to hit us even harder, trying to find the blogs that aren't already locked down. It doesn't matter to them; we have to work twenty times harder to block them than they do to hit us.
I, like Phil, have implemented rules in userContent.css that will alert me when a link has rel="nofollow" set. However, my rules are not quite as annoying as his. I think I will most likely never use nofollow in linking to other sites (as Phil says, I stand by
those I link to), but I already use it in one automatic application: TrackBack links. I don't want search engines indexing my TrackBack URLs, and I don't know another way to do that. (I don't know that this will actually work, but it won't hurt.)
I don't know the answer to referrer spam, but it's not going to come from Google. If there is an answer, it's going to come from within the Blogosphere.
Laurabelle's Blog says:
Google and comment spam
This weekend I noticed that Googlebot had started indexing the URLs of my newly renamed comment script, even though it...