The notion of a "worship leader" who leads the "worship" part of the service before the sermon (which, then, is no part of worship!) is so bizarre, from a New Testament perspective, as to be embarrassing. ... I know that "worship leader" is merely a matter of semantics, a currently popular tag, but it is a popular tag that unwittingly skews people's expectations as to what worship is. At very least, it is misleadingly restrictive.
He then follows this up with a footnote:
Perhaps this is the place to reflect on the fact that many contemporary "worship leaders" have training in music but none in Bible, theology, history, or the like. When pressed as to the criteria by which they choose their music, many of these leaders finally admit that their criteria oscillate between personal preference and keeping the congregation reasonably happy--scarcely the most profound criteria in the world. They give little or no thought to covering the great themes of Scripture, or the great events of Scripture, or the range of personal response to God found in the Psalms (as opposed to covering the narrow themes of being upbeat and in the midst of "worship"), or the nature of biblical locutions (in one chorus the congregation manages to sing "holy" thirty-six times, while three are enough for Isaiah and John of the Apocalypse), or the central historical traditions of the church, or anything else of weight. If such leaders operate on their own with little guidance or training or input from senior pastors, the situation commonly degenerates from the painful to the pitiful (From Worship by the Book, p. 47).