Jeff Sutherland explains the benefits of estimating software projects in story points.
In fact, a manager's Gantt Chart will never survive contact with the battle of project delivery. Jeff also points out that few companies know the velocity of their teams until they implement Scrum.
Jeff and some other members of the Scrum Foundation now teach that you can do estimation in three ways.
1. Backlog in story point and no tasking (hyperproductive teams)
2. Backlog in story points and tasks in story points (best current practice as teams are getting better)
3. Backlog in story points and tasks in hours (the old way)