Just about everyone working in the games biz had heard the heart-warming tale of Ethan Nicholas. He wrote an iPhone game (a tank simulation called iShoot), which duly sank into the soft eiderdown of iTunes obscurity. Then, he improved it. The game sank further. Then he released a free demo of the game. The full-priced version shot to number one, and is currently earning Ethan a tidy $20,000 a day.
The moral of this story is not that writing games can easily make you rich but that giving away games - or at least bits of games - just might add a little swagger to your trip to the bank. Demos make sales.