As far as Karen Armstrong goes, I have issues with her assumptions and methodology, and I told her that at a conference once. Good professional historians, especially religious historians (of which I am one), have to be careful to not let their biases show. Armstrong's biases are so blatant they detract from any valid point she may have.
Have you read her book "The Bible - an autobiography?" I'm reading it and it seems that she believes that the Bible should be read as poetry or myth, that there is no literal truth in it. I think she is play good cop/bad cop with the atheists. It's that or she's attempting to create a meta world religion based on the golden rule. I have read other accounts that say she is playing with history like putty, shaping and twisting it to her own ends. And I do agree with you that she has a strong bias: politically left of center for all her snipping at Bush, at Christian fundamentalists and apologizing to Islam. I'm curious to know what you think of her.