[incredulity]You believe the Devil is bound now!?[/incredulity]
You may be as incredulous as you want, but start with the simplest idea of what limits Satan. When few follow God, Satan/his demons are able to enter many. When the Church grew, Satan's ability to possess people was limited. When the Church is strong, Satan's ability to deceive the nations of the world is greatly reduced. When the Church goes weak, he will be able to freely deceive the nations.
Acts records Jesus' words explaining to Saul how the preaching of God's word increases light in the world as opposed to the darkness and power of Satan.
Acts 26:15“ ‘I am Jesus, whom you are persecuting,’ the Lord replied. 16 ‘Now get up and stand on your feet. I have appeared to you to appoint you as a servant and as a witness of what you have seen and will see of me. 17 I will rescue you from your own people and from the Gentiles. I am sending you to them 18 to open their eyes and turn them from darkness to light, and from the power of Satan to God, so that they may receive forgiveness of sins and a place among those who are sanctified by faith in me.’
So in the context of Revelation 20, Satan is not bound completely, but is limited in his reach with the strength of the Church. Further look to scripture to see that Jesus while in heaven still reigns and leads the Church.
1 Corinthians 15:20 But Christ has indeed been raised from the dead, the firstfruits of those who have fallen asleep. 21 For since death came through a man, the resurrection of the dead comes also through a man. 22 For as in Adam all die, so in Christ all will be made alive. 23 But each in turn: Christ, the firstfruits; then, when he comes, those who belong to him. 24 Then the end will come, when he hands over the kingdom to God the Father after he has destroyed all dominion, authority and power. 25 For he must reign until he has put all his enemies under his feet. 26 The last enemy to be destroyed is death.
Lastly, think about Christmas. If the Son of God was able to live as man on earth, then why not Satan? When Jesus came there followed a great expansion of his Church. A time will come when Satan will live on earth and cause a great deception to the world. This will be the time when he is let loose. That means he will not be bound anymore. That means he is bound right now. That does not mean he has no influence right now. It is just limited, but be prepared for the days of Satan. They will have many great trials.