"The binding of Satan means the coming of Christ, His presence on earth, the exercise of His power among men, has accomplished a defeat of Satan so that his power is broken. Satan is bound."– George Eldon Ladd
Ladd, the eminent NT professor who is now home with the Lord, is explaining in what ways the Kingdom has come Today. Though it's fullness is for the Age to Come, the "power of Satan has been broken because in some sense Satan has been bound and men and women may now be delivered from bondage to satanic power. Satan is a defeated enemy; and because of the work of Christ I may be delivered from the power of darkness and brought into the Kingdom of God's dear Son."
Makes me wonder if we shouldn't spend time "binding" the Devil (since he's already been bound, though not the final binding that Rev. 20:3 speaks of), and that we should instead give our time to helping to rescue the men and women that were the "strong man's goods" (Matt. 12:29).
[EDITOR'S NOTE: Read the COMMENTS for a discussion on what "binding and loosing" likely refers to in Matt. 16 and 18. Those who were raised on "spiritual warfare" language– as I was– beware. This might turn a few things around.]