Jonathan mentioned it below; the text of the policy is here. This gist of the policy is that DOJ will invoke the privilege only where it's reasonably needed, not reflexively, and that a lot of high-ranking DOJ officials need to evaluate and review each internal DOJ request to invoke the privilege, with the final decision coming from the Attorney General. The standard seems reasonable to me; all that internal review sounds pretty time consuming, but then I suppose they can amend the policy down the road if it ends up taking too much time.