Computer and Video Games has an informative post about Dwarf Fortress, saying the game is actually making money, in spite of being completely free to play (thanks Joao). Word is the game survives thanks to user donations, and after averaging over $3200.00 USD in donations over the previous four months, the game actually took in over $16,000.00 USD in donations in the month of April. On a related note, the Dwarf Fortress Website now offers a new version 0.31.04, which can be found in this forum post.