Allows you to hide the top admin bar in WP 3.2+ on the public site by changing user preferences en masse for both existing and new users.
No, it only changes user preferences so that the admin bar is hidden by default. Users can restore the admin bar in their individual preferences by choosing "Show Toolbar when viewing site" if needed.
If the admin bar is turned off but appears anyway, try logging out and logging back in. It also seems to turn itself back on if you have multiple sites running on the same domain with different admin bar preferences.