http://www.majordojo.com/projects/movable-type/custom-header/
The Custom Header Plugin for Movable Type makes it easy for users to upload and customize the header for their blog. It uses javascript and Ajax to make the customization process as seamless, intuitive and painless as possible. No knowledge of HTML or CSS is required, but the theme you are using must explicitly support this plugin.
Looks to be compatible with the iTheme themes http://ithemes.com/movable-type/ ... could we make our themes work with this?
Shouldn't be hard. I intend to make it work.