I am a Japanese web programmer.
http://php-web.net/ (written in Japanese)
I am the author of a plugin ShowID for Post/Page/Category/Tag/Comment.
This plugin shows post/page/category/tag/comment/media/user IDs on admin's edit post/page/category/tag/comment/media/user pages. You can see the ID when you visit an edit post/page/category/tag/comment/media/user page. This plugin requires WP2.9 or later.