As a small girl, my mother had often taken me to Pentecostal meetings. There I've witnessed people clapping, shouting and jumping. I used to wonder whether itís really true or they are just acting. Then years later, I went to this fasting prayer by a popular evangelist in tamilnadu, India. During praise and worship, I was clapping casually. Before I could realize, I started clapping so hard as if someone's forcing me to clap. I couldn't understand the power before behind this act. Only sometime later did I realize that what I experienced was the power of the Holy Spirit. It was this experience that made me realize that the doubts I had as a child was wrong and people do experience such power in their worship.
Many people are critical about the clapping in the spirit, prophesying, visions, etc. I feel its better not to be judgmental about these things. Paul says in his letter to the church of Corinth that some have been given the gift of prophecy, to some the word of knowledge and so on. See, itís only "some" and not all. So it means that if we aren't experiencing the power or gifts of the spirit, doesn't mean that others are not experiencing the same. Therefore we do not have the right to judge them in this regard.
The keyword is whether they are acting or not, they have to present accountability to God and so do we. So we need to be clean in the eyes of God. Itís advisable to stop ourselves from being judgmental.