He's recently been interviewed by Ted Olsen in Christianity Today. A couple of quotes from the article:
...we have to make sense of statistics for ourselves, applying our own experience. If I went to a group of Christians and made some sort of outlandish theological or political statement, they would question it. But if I put it in numbers, people would tend to accept it without discernment.
Rather than picking which statistics we agree with, we should be a little more agnostic about all of them. You don't have to believe them. Christians are called to accept and love people unconditionally. That doesn't apply to statistics. We should be cranky and judgmental.
There's another article on the subject on the CT site, by Ed Setzer. This one comes from earlier this year, and is entitled Curing Christians' Stats Abuse. He deals nicely with some typical 'myths':
"Christianity will die out in this generation unless we do something now."
"Only 4 percent of this generation is Christian."
"Ninety-four percent of teenagers drop out of church, never to return again."