Hashcash does indeed aim to prevent it. If you don't provide a valid hash, your message is rejected. nofollow tries to work around an accept-by-default policy.

Yes, people who use Google may reap some benefit — at least, they might once the amount of abandoned but commentable blogs has sunk enough that nofollow actually makes a difference. Make no mistake, we're talking about a pretty large time scale here.

Comment spam is not useful solely because it influences rankings. Does anyone rank anything based on the content of your inbox? Yet email is flooded with spam. Sure, the fact that comment spam can be used to game search engines is a nice bonus and currently an important reason to deploy it, but if that incentive disappears, comment spam will nofollow into demise. It's here to stay.

The bottom line is: nofollow does not benefit a blog owner. Unlike other options which do. So by and large, nofollow is irrelevant on the spam front. It is only going to change the way the web works outside of spam: like the horde of bloggers who rejoiced that now they can link to the people they're deriding without improving the linkee's ranking. Sigh.

Makeshifts last the longest.

One minute you're saying the individual blogger cannot benefit from nofollow, the next you're saying that bloggers are rejoicing because they have more control of ranking they indirectly award to sites they link. (Of course, maybe you think those bloggers are silly to think they are significant in any way.) Which one is it?

I never claimed nofollow was some sort of panacea. nofollow makes spam less profitable, period.

Hashcash users cannot reject an unstamped (or invalidly stamped) message outright. When everybody uses it and software becomes better trusted and debugged, they will; but until then the only reasonable way to use it is with a scoring filter, and never set the scores high enough that the binary decision about a message is made solely by its hashcash status. "Make no mistake, we're talking about a pretty large time scale here."

I also never claimed comment spam was useful solely because it influences rankings. (I don't know why you insist to think that I did.) Spammers will spam where they expect return on their investment. Period. What I do claim is that comment spam's ability to influence rankings — and especially to "hijack" the top hits in large search engines — is an entirely new class of opportunity for spammers, which gave them hella lot of incentive to start doing it. Of course there's inertia, and of course they won't stop just because you take some of the profit away. If suddenly litigation rises a hundredfold, spam won't stop either. But all other things being equal, I believe that it will slow down.

There is no contradiction in what I wrote. The individual blogger does not benefit from nofollow. I don't want to read spam; not even to delete it from the moderation queue. The less of my time spammers can occupy, the better. I don't even want to know that a spammer is trying to dump a pile on my web log until I check the logs of deflected spam attempts.

The fact that nofollow enables highschool antics and popularity contests is beside the point. It is not a benefit.

Hashcash in email is problematic and a long-term undertaking indeed, but I'm talking about hashcash on web logs where it is 100% reliable. It does present problems for those with Javascript disabled, but that's a different class of problem.

Yes, spamming comments to influence search engine results is a distinct class of revenue generator indeed — and one that's here to stay: there are millions of unattended blogs which are going nowhere and will not be implementing nofollow anytime soon.

Makeshifts last the longest.