GtkFileChooser should be able to show file sizes and other file details.  Right now, if you want to know what the file size is you have to go outside the file chooser dialog to find out what the file size is.  So, if you are in your email program, and you go to attach a file, you have to look in nautilus or run ls to make sure that the file is small enough to be reasonable for emailing.  

I think that there should be a way for GtkFileChooser to display the file size.  One possible UI for this would be right click on the bar that has "Name" and "Modified" and bring up a list of checkboxs for the details that are desired such as file size.  

This has been complained about previously at:
http://forums.mozillazine.org/viewtopic.php?f=7&t=318860&st=0&sk=t&sd=a&start=30
http://changelog.complete.org/posts/449-fromdrupal.html#c18918