I found that to be one of the more interesting metrics shown - but have to agree with everyone else as to how that is calculated. That said, anecdotally, it seems to jive up with experience, but who knows.
Definitely couldn't agree more. I think there's a little bit of a prerequisite that I kinda set for myself, and that people need to keep in mind, which is basically that the 40 hour week works amazingly well so long as you're not blowing 5 hours a week on Facebook. I try to keep extremely focused, which means 40 hours is about my limit before I go bonkers and become ineffective.