Index: wp-includes/js/plupload/wp-plupload.js
===================================================================
--- wp-includes/js/plupload/wp-plupload.js	(revision 28730)
+++ wp-includes/js/plupload/wp-plupload.js	(working copy)
@@ -218,6 +218,7 @@
 		this.uploader.bind( 'UploadProgress', function( up, file ) {
 			file.attachment.set( _.pick( file, 'loaded', 'percent' ) );
 			self.progress( file.attachment );
+			$('.upload-dropzone').append('<div class="spinner" style="display:block"><\/div>');
 		});
 
 		this.uploader.bind( 'FileUploaded', function( up, file, response ) {
@@ -249,6 +250,7 @@
 				Uploader.queue.reset();
 
 			self.success( file.attachment );
+			$('.upload-dropzone .spinner').remove();
 		});
 
 		this.uploader.bind( 'Error', function( up, pluploadError ) {