Index: wp-includes/js/autosave.js
===================================================================
--- wp-includes/js/autosave.js	(revision 7640)
+++ wp-includes/js/autosave.js	(working copy)
@@ -8,6 +8,9 @@
 
 	//Disable autosave after the form has been submitted
 	$("#post").submit(function() { $.cancel(autosavePeriodical); });
+	
+	// Autosave when the preview button is clicked.
+	$('#previewview a').click(autosave);
 });
 
 // called when autosaving pre-existing post
@@ -89,6 +92,7 @@
 			getpermalinknonce: jQuery('#getpermalinknonce').val()
 		}, function(permalink) {
 			jQuery('#previewview').html('<a target="_blank" href="'+permalink+'" tabindex="4">'+previewText+'</a>');
+			jQuery('#previewview a').click(autosave);
 		});
 	}
 }