While working with different themes and plugins sometimes you need to know ID of certain post, user, category etc and for that you have to go through many clicks. By displaying IDs on WordPress Admin Area, side by the default lists of posts, users, links, categories, pages etc you can easily grab the ID you are looking for.
All you need to do is install and activate WP Show IDs ( Simple, Yet Elegant ) plugin. It works both in single and multisite WordPress installations and displays IDs almost everywhere including custom post types and taxonomies.