"Net" is in the eye of the beholder. If an author wants a piece of the action, gross is the only number to use. They probably won't give it to you, but from everything I've heard, no movie has ever made money once the studio lawyers and accountants are through with it.
Absolutely, and even then that's no guarantee - New Line cinema are currently being sued by the Tolkien estate for $150mil of their gross profit participation in the Lord of the Rings films. Then again, New Line have also been taken to court by Peter Jackson and Saul Zaentz (three times I think in the latter case) for failing to either pay out what the plaintiff is due or open up their accounts for the outside financial scrutiny required to determine what monies are due.
One upbeat note to all that is the latest WGA contract ratified this week does allow greater access to the studio books than ever before.