Can already toggle by opening up a second browser that you never use (and you clear cookies and history after each use). You'll still get geographic filtering but little else. Webmasters do this all the time when checking out how well individual pages rank for various keywords.
Of course, your idea of a visible toggle switch is far more user friendly.
EDIT: added "history"
Isn't it that simple like pausing and clearing your web history in google? https://www.google.com/history/
Re:The real Filter Bubble debate
by icedpulleys on Friday June 24, 2011 @10:14PM
(#2694714)
Open an incognito window in Chrome, don't log in to your google account, and search there.
Random aside: one of the most annoying happenstances of the modern interweb is the prevalence of those ads that follow you around especially because they're really poor at being relevant.