A really cool feature for custompress custom fields would be to be able to use the title from another custom post type as options in a select/multi select. As an example:
create a make custom post type
create a make with title Chevy, Nissan, etc
create custom post type called Car
add custom field to car and have an option in the field type to use the Make custom post type as the options in a dropdown so it woul auto populate with all post title from the Make post type.
I've made a custom plugin that does the same...sure you know logic is pretty straight forward in the custom post definition:
$makes = get_posts('post_type=make&numberposts=-1');
then loop it to display options