Wouldn't it make sense to list all image sizes when you are adding an image via the uploader. Right now it only lists the default sizes in
$size_names = array('thumbnail' => __('Thumbnail'), 'medium' => __('Medium'), 'large' => __('Large'), 'full' => __('Full Size'));
But with the introduction of
add_image_size, it would be helpful if that list included the new image sizes that theme authors create.