In regard to this, my advisor remarked about the negative effects of the "gentlemen's agreement" among many schools to not require a decision from any postdoc candidate until after the winners of the NSF postdocs are announced; the downside being that it delays the game somewhat and makes for a flurry of activity during the weeks proceeding the announcement of the NSF postdocs (which was about two weeks ago). Since the usual time period one is given to consider an offer is about two weeks (at least that's what I've heard), it seems that third round offers should just be starting.