Spam is the scourge of the internets. It clogs Internet Tubes all over the globe, overloading the trucks that take internets around the world.
And it is directly caused by Google's PageRank and Adsense systems. They (as well as others, but primarily Google - take a look at any spam farm, and you'll see prominent Adsense ad blocks) created this mess by enabling individuals to cash in on hijacking innocent websites that have enabled anonymous commenting.
A spammer can sit in his basement, run some scripts to find juicy targets, send out some probes, then unleash hell in the hopes that they will improve the PageRank of their (or their client's) websites, in an attempt to increase Adsense revenue on those sites.
So, here's the easy solution. If a website is shown to be associated with spammish activities, the Adsense account is suspended. And their PageRank is reset to 0. Take away the financial incentive, and the rules of the came change.
It's time for Google to step up and show some corporate responsibility. The whole rel="nofollow" solution is a non-starter, since it only works if we all agree to break the nature of the web in the first place by devaluing all links contributed to a website. It's not worth throwing the baby out with the bathwater.
Now, how to define "spammish activities" - and, who gets to determine if a spam producer is guilty of that? There could be juries. There could be committees. Heck, it could become a social software tagging exercise, where the intelligence of the hive is harnessed to determine if something is spam or not. spamornot.com? Have an appeals process, to prevent abuse. Have a responsible governance system to ensure effectiveness.
It seems to me that it would be in Google's best interest to protect the value of PageRank and Adsense. By allowing spam farms to co-opt both systems, they devalue both. By ensuring spammers are removed from the system, we're left with a more realistic representation of the online advertising ecosystem, with (hopefully) better representation of the actual contributors and participants.
But, this has to stop. Now. It's only getting worse, and is threatening to smother any semblance of openness left on the web (1.0, 2.0 or beyond).