There is little better than someone who loves their work:
For the past few weeks I’ve been working with a fellow developer on a project that required an all-out programming effort. It’s done now, so we’re back to a regular schedule, but when people hear about the crazy hours they often say they’re sorry. They really shouldn’t be. I would never do this often, or for long periods, or without proper compensation if done for an employer, but the truth is that these programming blitzkriegs are some of my favorite periods in life. Under the right conditions, writing software is so intensely pleasurable it should be illegal.
(Via Daring Fireball)