No no no no no.
*I am not applauding that at all, no I am not*
Clapping is not appropriate. Here is why. Even if one acclaims a particularly fine rendition of a hymn, the object of praise must always be God. So to "applaud" the singer, for example, one would traditionally shout "Amen," "Praise God," or "Hallelujah!" One is then complimenting the giver of the homily, hymn or musical for their fine contribution in praising God. That translates as praise to the performer for having done such a fine job of serving to praise God. And another thought. While in a concert hall it is talent you are applauding, but in a church the singing is display of a gift from God, and therefore praising God (for giving the speaker the words and the singer the talent) is most appropriate. So those of you who have desire to praise a particularly fine homily and cannot restrain yourselves, I suggest one of the three exclamations above. Further, if you attend a Mass where the pastor is actually soliciting applause (argh) I suggest you help him with his humility with responding with one of the above instead of applause. Here in the South I know some very prayerful and vigorous Baptist or non-denominational services where Catholics could go for quick instruction how to loosen up on their ability to shout "Hallelujah" instead of clapping, ha. That would not be such a bad thing as they recall it's the praise of God, not the praise of the talent of God's worship leader.