Attendees at WonderCon, opening today in San Francisco, will receive a free Iron Man 2 mini-poster featuring Scarlett Johannson as Black Widow while supplies last.  This juicy premium will be only one factor helping to draw crowds; attendance is already on a strong upward curve.  The show grew from around 20,000 in 2008 to around 34,000 last year, with big increases in space helping to provide a venue for stronger screenings and panels (see “WonderCon Gets More Space”).