I have had to use this little bit of code a few times for multiple clients who didn’t want the new WordPress 3.1 admin bar. All you need to do is add this snippet to your theme’s functions.php and all of the admin bar functionality will be removed:

/* Disable the Admin Bar. */
add_filter( 'show_admin_bar', '__return_false' );
remove_action( 'personal_options', '_admin_bar_preferences' );