I've read about it and now I've experienced it myself. I got hit by nasty referer log porn spam today. I just checked a couple blogs over at FreeRoller and they got hit by the very same thing.
I guess I need to get busy again. I'm working on a fix for referer spam in Roller 0.9.7. Roller will check the validity of each referer ensuring that the refering page exists and that it contains a referering link. Roller will also have the ability to ignore URLs that contains certain key words.
UPDATE: today's spam is coming in from a site called voodoomachine and another site whose name is a just little too nasty to mention. It does not appear to be a one time thing, the hits are still coming in from the spam machine. What a drag. If this continues throughout the day, I'll be taking the referer log off of my page template. What a drag.