Many plugin developers (Mark points out Automattic as an offender) place links to their plugin setting pages in the admin menu; before posts, links, pages and comments. It is highly unlikely that you will click on any plugin in the admin area more than posts and pages. Menu Humility addresses this small issue by bumping the links to plugins to the bottom of the menu.
Ryan Imel recently noted it as a Sweet Plugin Of The Day and recorded a great little video that walks you through exactly what it does.
Link: Menu Humility