It's a great read (Brooks is an excellent writer), and contains some top quotes. For example:

• "Adding manpower to a late software project makes it later."
• "Cost does indeed vary as the product of the number of men and the number of months. Progress does not. Hence the man-month as a unit for measuring the size of a job is a dangerous and deceptive myth. It implies that men and months are interchangeable."
• "The bearing of a child takes nine months, no matter how many women are assigned. Many software tasks have this characteristic because of the sequential nature of debugging."

Make your managers read it!