Here's a simple little plugin that adds a keyboard shortcut for toggling the visibility of the admin bar on the front end of your site. It's good to note that it toggles visibility by simply adding/removing a
display: none; on the element. Thus, it doesn't change your profile setting for admin bar visibility. Could be a handy little tool when developing and designing.
Here's a peek at Apermo AdminBar Toggle by Christoph Daum