I think one of the most spiritually dangerous practices today is encouraging people—in small groups or in front of the church or even in print—to talk about how God has transformed them. They are told to explain how they used to have a bad temper or a problem with porn or were stingy or had one bad habit or another—and through prayer, effort, and grace, they have been changed. The formal glory all goes to God, of course, but the focus unfortunately is often on the self—on how I have been changed.
Those who share such testimonies cannot but be tempted, as was the Pharisee in Jesus' parable: "Lord, I thank thee that I am transformed, that I am not like this untransformed fellow next to me." And those who hear such testimonies find themselves praying, "Lord, why am I still struggling with this and that; why am I not like this transformed person?"
Granted, the point of the testimony is to encourage people, to remind them that God is great and that we can be transformed. In this respect, I am a great fan of testimonies—we publish them in Christianity Today whenever we find really good ones. But unless they are crafted and framed just so, they tend to have this deleterious effect: they encourage narcissism and anxiety. And they tend to prompt people to reach down to their bootstraps to pull themselves up.
What's interesting about the classic biblical testimony—Paul's conversion (Acts 9)—is that it spends little space on transformation as such and a lot of space on what happened: an encounter with the gracious and resurrected Lord. When Paul repeats his testimony (Acts 22 and 26), his speech assumes a transformation—from persecuting Christians to proclaiming the Christian gospel—but does not focus on it as such. He does not say, "Look at how I've been transformed by the grace of God!" He is simply explaining why he now preaches in the name of Christ. The narrative structure of his story is his transformation, but the real subject of his story is Jesus Christ.