The tech graveyard is full of overworked, tired, run-down, exhausted people who put in more hours than their bodies could handle. I run into people all the time who are putting in ridiculous hours and getting no where.
Hours don't make it. Good choices, the right focus, and intelligent decisions over a long period of time make it.
Jason C's point about practice is absolutely right though. But practice doesn't equal long hours. Practice equals practice. 3 hours of focused practice on the right thing is far better than 6 hours of practicing the wrong thing. Practice quantity isn't the secret, it's practice quality.
Here's a related post I wrote on "Making money takes practice like playing the piano takes practice":
http://37signals.com/svn/posts/1985-making-money-takes-pract...