The real significance of File Vault is that it makes the Mac the first OS that protects privacy, rather than just security. For those who have not considered the difference, security is a scheme that ensures that only your corporate masters can find out what you are up to. Privacy means that only you can see what you are up to.
Perhaps the biggest difference between Apple and Microsoft has traditionally been that Microsoft supports corporations and Apple supports individuals. File Vault once again brings that difference into sharp focus. It actually has the potential to hurt sales to corporations that reserve their right to spy on you—hence the marketing spin that this is to protect corporate secrets on the road—but it once again clearly illuminates Apple as one of the good guys, a force in the world to slow down the seemingly inevitable advance of our Brave New World.
from an article by one of the original Mac interface designers.