|The Execution of Robespierre from Wikipedia|
Here's a paragraph from Erickson's book:
The first human trial of the guillotine in April of 1792 was something of an experiment, which gave the many spectators an added frisson. The machine had been used on sheep and calves, and tested on human corpses brought from the charity hospitals. But no one could be certain that it would work as efficiently on a live criminal, and the wretched forger scheduled to be executed that day must have suffered the added torment of doubting the efficiency of the savage blade. Scientists speculated about whether the head might live on after it was separated from the trunk, whether the mind might go on thinking, the eyes seeing, the tounge wagging. But the forger's execution proved to be effortless and swift, and made a very good show, and the observers went off afterwards satisfied that they had witnessed a new and entirely satisfactory form of public vengence.
The guillotine has continued to be used, even in my lifetime! I found a date (at the site mentioned later in this paragraph) that shows the guillotine used in 1987 in East Germany. And, it was last used in France in 1977 when the murderer Hamida Djandoubi was beheaded. (information from About.com) The debate as to whether or not the person continues to be alive for seconds after the beheading has continued to be debated. For more information on that, you can read this article at The Guillotine site.
Of course, Marie Antoinette faced the end of her mortal life lying on a guillotine platform. Her husband, King Louis XVI, had also been executed in this manner nine months earlier.