I looked the prize up in Wikipedia and discovered it's been going on for years. Some previous winners:
2006 — The Stray Shopping Carts of Eastern North America: A Guide to Field Identification — Julian Montague
2005 — People Who Don't Know They're Dead: How They Attach Themselves to Unsuspecting Bystanders and What to Do About It —Gary Leon Hill
2004 — Bombproof Your Horse — Rick Pelicano and Lauren Tjaden
2003 — The Big Book of Lesbian Horse Stories — Alisa Surkis and Monica Nolan
2002 — Living with Crazy Buttocks — Kaz Cooke
Wikipedia reports that submissions are sent in by librarians, publishers, and booksellers. The winner is selected by public vote.
Sounds like a lot more fun than most ballots.