Project Honeypot provides a method to steer known spammers away from websites altogether - though this does not remove the need for protection from new miscreants. More exactly, known offenders can be redirected to an error page regardless of which page they intended to land on.
This system works only as long as the community (websites) provides honeypots for the would be spammers to fall into. The data gathered by the honeypots provide the basis for a blacklist of IP addresses used by frequent spammers and email or link harvesters.
Server side code (PHP, asp.NET, "classic" asp, ...) is used to check the users IP address against the blacklist when the user arrives on the site, and if applicable can redirect the user to an error page or legal statement.
Full details of Project Honeypot are at www.projecthoneypot.org.