Richard Smith, former editor of the British Medical Journal and regular critic of the pre-publication peer review process, writes on the subject of post-publication peer review.
But more important than...formal types of peer review is the informal, the thousands of comments, decisions, and actions from the many that lead to a sorting of studies. I may hear a study presented or read a paper and be impressed. Others in the audience or other readers might also be impressed. We talk to friends about it. We email colleagues. We put it on listserves. Some of the recipients are impressed and start their own cascade. Others are less impressed and see problems. Perhaps a statistician attracted by the clamour reads the clinical article and sees important flaws that she shares with colleagues. Somebody might incorporate the study into a lecture, a review, or a grant application. And so a study might attract increasing attention and assume a prominent place, or it might fade as its receives more attention and more problems are noticed.
Many studies, in contrast, attract no attention—usually, but not always, rightly.