My initial reaction to much of the Purpose-Driven movement was that there is a fair bit of wisdom there, but little that is distinctively Christian. There is little emphasis on doctrine, and actually the book Purpose-Driven Church would work pretty much just as well for a mosque, synagogue or health club. And quite a few of the organisations that subscribe to the Purpose-Driven philosophy seem somewhat batty.
Over the last few weeks, I've seen some more of the movement. I've read bits of Doug Fields' book Purpose Driven Youth Ministry, and I've met and heard talks by some of the Purpose Driven Worship team from Highlands Fellowship, whose website includes this rather strong recommendation of Rick Warren's work:
God had given Pastor Rick Warren his plan for our generation, and now Jimmie knew that God had the same in mind for the church in Abingdon. [That's Abingdon, Virginia, USA, not the original one.]
And I have to say (despite the above quote) that I have been generally very impressed by what I have seen. Both groups - both Doug Fields and the folk from Highlands have stressed the importance and priority of the youth worker / music group member's relationship with and dependence upon God even above their skill as a youth leader or musician. Both of them seem to be using the "purpose-driven" approach simply to mean the importance of thinking through what you are doing and the way you are doing it beforehand, and aiming it all to God's glory.