For 102342 invocations of TreeItem#setImage on Windows:

            time (ms)
unpatched     1923
patched        786

--- Tree.java.original	2008-03-25 19:19:34.419600000 +0200
+++ Tree.java	2008-03-25 19:19:28.808600000 +0200
@@ -3526,13 +3526,19 @@
 
 int imageIndex (Image image, int index) {
 	if (image == null) return OS.I_IMAGENONE;
+	boolean updateImageList;
 	if (imageList == null) {
 		Rectangle bounds = image.getBounds ();
 		imageList = display.getImageList (style & SWT.RIGHT_TO_LEFT, bounds.width, bounds.height);
+		updateImageList = true;
+	} else {
+	    updateImageList = false;
 	}
 	int imageIndex = imageList.indexOf (image);
-	if (imageIndex == -1) imageIndex = imageList.add (image);
-	if (hwndHeader == 0 || OS.SendMessage (hwndHeader, OS.HDM_ORDERTOINDEX, 0, 0) == index) {
+	if (imageIndex == -1) {
+	    imageIndex = imageList.add (image);
+	}
+	if (updateImageList && (hwndHeader == 0 || OS.SendMessage (hwndHeader, OS.HDM_ORDERTOINDEX, 0, 0) == index)) {
 		int /*long*/ hImageList = imageList.getHandle ();
 		int /*long*/ hOldImageList = OS.SendMessage (handle, OS.TVM_GETIMAGELIST, OS.TVSIL_NORMAL, 0);
 		if (hOldImageList != hImageList) {
--- TreeItem.java.original	2008-03-25 19:19:45.379600000 +0200
+++ TreeItem.java	2008-03-25 19:19:41.316600000 +0200
@@ -1634,7 +1634,14 @@
  * @since 3.1
  */
 public void setImage (Image [] images) {
-	checkWidget();
+
+    /*
+     * It doesn't make sense to checkWidget() here because the method just
+     * delegates to another method and doesn't use the instance state before
+     * doing so i.e. if checkWidget() is at all necessary, it will be performed
+     * by the called method. 
+     */
+	// checkWidget();
 	if (images == null) error (SWT.ERROR_NULL_ARGUMENT);
 	for (int i=0; i<images.length; i++) {
 		setImage (i, images [i]);
@@ -1684,12 +1691,11 @@
 		images [index] = image;
 	}
 	if ((parent.style & SWT.VIRTUAL) != 0) cached = true;
-	
-	/* Ensure that the image list is created */
-	//TODO - items that are not in column zero don't need to be in the image list
-	parent.imageIndex (image, index);
-	
+
 	if (index == 0) {
+	    /* Ensure that the image list is created */
+	    parent.imageIndex (image, index);
+
 		if ((parent.style & SWT.VIRTUAL) == 0 &&!cached && !parent.painted) {
 			return;
 		}
@@ -1714,7 +1720,13 @@
 }
 
 public void setImage (Image image) {
-	checkWidget ();
+
+    /*
+     * It doesn't make sense to checkWidget() here because the method just
+     * delegates to another method i.e. if checkWidget() is at all necessary, it
+     * will be performed by the called method. 
+     */
+	// checkWidget ();
 	setImage (0, image);
 }