What is r-e-f-e-r-e-r.com all about?

I've noticed a bunch of visits to several of my WP sites lately from http://r-e-f-e-r-e-r.com. Information on Google is somewhat sketchy but it seems to be some sort of "referral spam". Anyone know what this is all about? should I be concerned? Is it something beneficial or should I be trying to block it?