In his review of Your Brain on Music, John Walkenbach says:
many people have found that you can become an expert in anything if you devote a minimum of 10,000 hours to it. Assuming a 40-hour week, you can become an expert at something in about five years. If you’re not working at it full time, figure three hours per day for ten years.
In the Freakonomics post, Dubner says:
excellence is accomplished mainly through the tenets of deliberate practice, which are roughly:
1. Focus on technique as opposed to outcome.
2. Set specific goals.
3. Get good, prompt feedback, and use it.
I don’t have much to add by way of tying all this together except for my fascination with the subject and with people who have devoted themselves to something so profoundly that they transform themselves.