What does the year 2007 hold? The Magic 8-Ball says, "Ask again later." My own reluctance to begin is indicated by the piles of unopened mail on my desk. Indeed, much of this week has been devoted to visiting exhibitions at the end of their run, before it is too late. "Vollard" closed at the Metropolitan Museum this Sunday -- it opens at the Art Institute of Chicago on Feb. 17 -- and "Brice Marden: A Retrospective" closes next Sunday at the Museum of Modern Art.