What is the purpose of referrer spam?

[NobleSavage]

Why do people who do this? What are they trying to accomplish?

[matt]

In the 'olden days' referer spam was used by people to get backlinks to their sites. Lots of stats pages are indexed in google. These days it seems to cause more harm than good with search engines.

[virgohippy]

Some sites, blogs mostly, also do trackbacks, where they link back to referred hits.