This may be helpful to those WordPress developers who want to keep their site as it was without the new admin bar arriving with WordPress 3.1 soon.

Simply use this code in your there's function.php file or add it to a new file in the plugins folder and activate.

add_filter( 'show_admin_bar', '__return_false' );
remove_action( 'personal_options', '_admin_bar_preferences' );

WordPress How To: Disable the Admin Bar in WordPress 3.1