Groothuis remains one of the most clear-headed thinkers around. I learned great deal years ago from his earlier books on the New Age movement [Unmasking the New Age, Confronting the New Age, and Revealing the New Age Jesus, later revised and updated as revised as Jesus in an Age of Controversy and more recently from his book Truth Decay.] His blog post on Michael Shermer is worth reading. (HT: Wintery Knight).
I previously blogged about Michael Shermer and his debate with Greg Koukl on Hugh Hewitt's radio program here.