Try to open a directory witch big zip files (my case - 30 zip files with ~60000 files and directories, total size ~170M). Application is not responding for 2-4 minutes. With 1.6.0_01 works without delay. Windows XP.  

>java -version
java version "1.6.0_02"
Java(TM) SE Runtime Environment (build 1.6.0_02-b05)
Java HotSpot(TM) Client VM (build 1.6.0_02-b05, mixed mode, sharing)

Test code:
# FileChooser test
import java.util.*;
import javax.swing.*;

class test
{
   public static void main(String [] args)
   {
      JFrame frame = new JFrame();

      JFileChooser fc = new JFileChooser();
      int val = fc.showOpenDialog(frame);
      System.exit(0);
   }
}