Today I found my latest example of why we must guard our life and our doctrine closely. John Clark, a self-proclaimed "non-Christian servant of Jesus" has written his own version of the New Testament that omits the word 'church' on the basis that, as he says, "no mention of that beast exists anywhere in the original New Testament writings." He also seems to have problems with the doctrine of the Trinity (his no-Trinity view is the foundation of his denomination), the authority of Scripture as the Word of God ("To 'preach the Bible', as some boast of doing, is nothing."), and salvation by merit of God's grace ("There is no such person as a 'sinner saved by grace.") Boo.
Check out Off the Wire's thoughts on it. You'll find further observations on my part about Mr. Clark's teachings in the comments section.