Adding and removing a custom header image is significantly easier in WordPress 3.4.
The above silent video shows the customizer view in WordPress 3.4. You will see the preview of the site on the right side while options are on the left. The menu bar auto-adjusts as the image is removed and added.
The screencast was the first attempt on an iMac, using Quicktime player to create the video as well as uploading through a menu option.
Maybe the developers can add an option to fix the menus and widgets through this preview too.