Chicago’s Merchandise Mart gathers five art fairs under a single umbrella. “The centerpiece is Art Chicago, a stricken show the Mart took over in 2006 and defibrillated back to life. Last year’s Art Chicago drew more than 42,000 attendees. The 2008 version will have more galleries, art and space. Whether it is as successful for dealers as 2007’s may hinge on the mood for art in a dour world economy.”