I wanted to write a sharp, insightful, and illuminative post on the difference as well as the need for real confession. Instead, I'll post a link to seminary friend, Father Benjamin. He explains the difference most eloquently.
The key difference:
Yet confession offers something that other forms of self-accusation never could, reconciliation with God and with the community. There is no need for the whole community to hear a person's transgressions, and if they are good people, they aren't really interested. The priest takes the burden on himself, and hears the sin on behalf of the community and offers their forgiveness. More importantly, the priest hears the confession on behalf of God and offers his forgiveness, through a human voice and a human face...Thanks Father Benjamin!
The biggest difference between a online admission of guilt and Catholic confession is that the first is centered on the person and on their sin. Catholic confession is centered on the love and the mercy of God, made visible in the scriptures and in Jesus Christ. The sins a person has committed, no matter how terrible, are like drops of blood in the fire of God's love. In front of that, our sins don't stand a chance.