I was troubled with log spammers for a long time, and though there were quite a few referrers they seemed to all come from just a few IP's. Blocking the IP's with .htaccess did not stop the referral from showing up on the log, however shortly after I blocked them the referrals stopped. It's worth a try.
The IP's that I blocked for this were:
but they may be using others now...
These URL's seem associated and all this comes from (where else) China, though the referrers seem to be mostly European, .ne, .de, .fr, etc.
I once thought to complain to the sites being referred, but none had any contact information, which leads me to believe that the referred sites are being scammed by an seo firm or are maybe the victims of some click-fraud scheme.