On idioms: Before you can say Jack Robinson

Via ingoodfaith

'Yo ho, my boys!' said Fezziwig. 'No more work to-night. Christmas Eve, Dick. Christmas, Ebenezer! Let's have the shutters up,' cried old Fezziwig, with a sharp clap of his hands, 'before a man can say Jack Robinson!' (Charles Dickens,  A Christmas Carol, 1843)

Each language has certain words and phrases which cannot be directly translated into another language, because these terms or expressions have a figurative rather than a literal meaning. I'm talking about idioms or idiomatic expressions. I remember a little while ago that I was looking for a phrase in English to tell someone that she should make the most of her time back home, because she'll be back in Sheffield in no-time. In Dutch (my native language), I would say:

"Geniet ervan, want voor je het weet ben je weer terug in Sheffield"

which in English would literally translate as:

 "Enjoy, before you know it, you'll be back in Sheffield"

My intuition told me that 'before you know it' sounded somewhat odd in English (though I'm sure English speakers will get the gist), so I decided to look up the English idiom that would describe "in a very short time". I can't remember how I found it, but Google managed to provide me the expression "Before you can say Jack Robinson" to describe the exact thing that I wanted to say.

That's also how I came across The Phrase Finder, a wonderful resource that lists all the phrases and idioms in English. The great thing about this resource is that it gives you some information about the origin (etymology) of the word and meaning, although we'll never be able to check whether that information is correct or not. What made this expression all the more interesting is that it was recorded in one of the 18th century dictionaries that I study:

JACK ROBINSON, before one could say Jack Robinson, a saying to express a very short time, originating from a very volatile gentleman of that appellation, who would call on his neighbours, and be gone before his name could be announced (Francis Grose's Classical Dictionary of the Vulgar Tongue, 1785)

As with any slang dictionary, we don't get any information about the origin of the phrase. So who is this Jack Robinson person exactly? According to the Phrase Finder, there was a real Sir John Robinson who was the Tower of London Constable in the sixteenth century and had a notorious reputation for chopping many people's heads off. However, the Phrase Finder does call the link between this person and the coinage of this expression into question. Perhaps it's just another urban legend, and will remain so forever.

So just a question for my native English speaking friends or readers: Is this expression still commonly used today? Do you use this expression yourself?