A curious trend seems to be emerging - referrer spam. It's a bit niche, so it makes me think I'm missing something.
When you click a link on a web page, your browser tells the place you're going, where you came from (ie. it tells the destination what the referrer was). The spam technique is to change this so that it always says you came from the spammer's favourite web site.
Why would they do this? The only people that would know about the referrer are web site owners. Surely, that's a pretty niche, small audience (and probably the most scam-savvy).