i'm responsible for http://negimaki.com/ hosting a few hundred PixelPost 1.4.x sites and have been following this "referer spam" for quite sometime now. there's no "one-shot" solution for this problem. a combination of log analysis, adding firewall rules and such are just some of the many ways to slow down rampant occurance.

if you are running Apache and have access to httpd.conf or php.ini on a UNIX/Linux environment, you can use PHP's auto_prepend capability to with th following tools:

Referer Karma
http://unknowngenius.com/blog/wordpress/ref-karma/

Bad Behavior
http://ioerror.us/software/bad-behavior/

for another layer of protection, you can also use this tool to create special filters.

mod_security (an Apache module)
http://modsecurity.org/

if you are a server admin, you better get to work. and if you don't have access to those files, be sure to bug your service provider for it.