With WordPress 3.1 update Automattic Inc. has introduced new features like Admin bar, Post Formats, Internal Linking etc. The Admin bar feature is an easily accessible toolbar like nav bar on top of WP 3.1 blogs which can be displayed on blog homepage or admin edit dashboard page. The Admin Bar includes links to Comments, Appearance, Add New post, User settings etc. If you didn’t like the Admin bar feature then it can be disabled easily.
In order to disable the Admin bar head over to your user profile page by clicking Users > Your Profile from admin dashboard. On that page you will see the ‘Show Admin Bar‘ settings where you can enable or disable Admin Bar in dashboard and when viewing site. But if you have many authors or registered users then to disable Admin Bar for all users will be a tedious task. That is where your coding skills can help.
You add various codes to functions.php file of WordPress to get desired settings on blog. The Admin Bar can be disabled for all users or specific users alone. Check out this post on Yoast.com that provides code snippets which you can add to functions.php.