The idea, in a nutshell, is this: "Fix your ideal schedule, then work backwards to make everything fit – ruthlessly culling obligations, turning people down, becoming hard to reach, and shedding marginally useful tasks along the way."
Newport works between 8:30 and 5:30 on weekdays only, yet he gets a lot done:
This past summer, for example, I completed my PhD in computer science at MIT. Simultaneous with writing my dissertation I finished the manuscript for my third book, which was handed in a month after my PhD defense and will be published by Random House in the summer of 2010. During this past year, I also managed to maintain my blog, Study Hacks, which enjoys over 50,000 unique visitors a month, and publish over a half-dozen peer-reviewed academic papers.
Ramit Sethi of I Will Teach You To Be Rich wrote about Newport and a few other people who use similar techniques to get a lot of meaningful work accomplished in 40 hours a week or less.
I think they are onto something -- ever since I had kids (which gave me fewer hours in the day to work, and also put a start and end time on my day) I've been much more productive.