The plugin Media Custom Fields has a couple of minor errors, the Author seems non contactable. (plugin website down, authors blog has no contact info, no contact info within plugin readme etc.)
Error 1: When I first installed the plugin and no custom fields had yet been create a foreach error appeared.
Error 2: Once text has been entered into a custom field, it cannot be removed/left empty. When the image properties are saved the custom field contents simply reappear. (I have only checked this from Edit Post > Featured Image > Gallery (TAB).
Also there is very little guidance to usage in terms of printed material, whilst there is a video on vimeo nicely explaining how to use the plugin on an attachment/single pages, it did take me a little while to work out how to use the custom fields within the index/categories etc.
For reference to others here is the solution to grabbing custom fields for the post thumbnail (within the loop):
$thumbnail_id = get_post_thumbnail_id( $post->ID ); $tqmcf_disable = get_post_meta($thumbnail_id, 'tqmcf_custom-field-name', true);