Referer spam has been around since at least 2002 when Wired wrote "When the spam hits the blogs" and even interviewed little ol' me about it. The nuisance was taking off then, and as many blogs had automatically updating link lists on their blogs these might have been the ultimate target. Because honestly now, one person checking their logs on occasion does not a great target make. Similar tactics are used to do trackback spam, which then allows the spammed link to appear in the targeted blog.
Back in 2002, this is what Pollak said:

"On top of the fact that this is obnoxious and intrusive, it completely destroys the entire point of a referral log," said August J. Pollak, cartoonist for the XQUZYPHYR and Overboard blog. "If hundreds of spammers start spamming logs, then people will eventually stop using logs."

He was right, people don't really use referral logs in the same way anymore. Google analytics drops bot-like traffic so one doesn't have to bother seeing these links. So why are they still doing it? It causes damage to your site and rankings, while there's a slim chance your log files are public.

It's bots talking to bots now. It is as if we have the human web with cat images, conspiracy theories and news, while underneath all that there's bots clicking ads, sending spam, and hitting trackbacks. The ways humans wanted to interconnect our sites and topics, ruined by quick bots that overwhelm these trusting networks. Does it work? Perhaps, the spamming link seen in this screenshot that's doing it's worst today is attempting to hike up the price for a domain that is currently for sale. Sneaky.

How do you kill it? If you use awstats, you can stop referer spam with this. You can also if you have access to apache config files use this rather elaborate filtering system to block known names from ever touching your site, the usual libido rapido and porn names. You should.