Wow. Now here is a case of cooperation over competition. Six Apart, Google, Yahoo, MSN, WordPress, Userland and others worked together to support the nofollow tag to reduce the value of comment spamming.
UPDATE: Scoble makes a similar point to anti-links. Sunir, who is actively involved in fighting wiki spam, raises some really significant issues. Pete suggests VoteLinks to negatively rate spammers may be more effective.
Best thing about cooperation is that it can be built upon. Good thing too, as curbing link spam will take many iterations in practice and this is a change in the structure of the web itself.