While there are reasons for blinded (or double-blinded) peer review, there is also something to be said for "identifiable" peer review, especially in an open forum like PLoS ONE. If reviewers are identifiable, then concern for their own reputations will motivate them to keep their comments as constructive (or at least, valid) as possible. A glance at almost any internet forum will show how poor an online discussion can get when some participants feel they have nothing to lose.