At the Stack Overflow blog, Ryan Donovan muses on domain names bought and paid for, perhaps with a funny project or joke in mind, but either put to not good use or left altogether fallow.
For the record, I've had my share of goofy domains. Before joining Stack Overflow, I had robertstackoverflow.com, a stray thought that I decided to take too far and then gave up on when I couldn't suss out the video editing software. Speaking of dumb jokes, I also have allis.horse, after a conversation about horse cults. For my dad's birthday one year, he asked me to get him faciebookie.com because he hates Facebook and wanted to put up counter-programming there. Place your bets on its future, but nothing has happened with it so far.