This might actually be my favourite effect from Derren's 'Devil's Picturebook', but I can't help but worry about suggesting a spectator shuffle the deck.
Has anybody here tried out this little miracle and had a similar thought?

Joe

Beautiful! Spectator/audience management.

I have done this with family as well as simple effects that, I'm sure you would recognize, and have completely bamboozled them.

magic is in the presentation. This is not news.

You're absolutely right, so as a point would you suggest a shuffle at the beginning of the effect?

I know Derren lets the spec shuffle in the vid, but I would never take that kind of risk. Many specs don't know how to handle cards well, and even if you ask if they do, you can never guarantee they won't drop a bunch of cards (fail!) or else notice the nature of the deck (fail!). I do a couple of riffle shuffles that are obviously fair, and then ask one spec to give it a cut and then ask another to cut it somewhere else in the deck. It involves the audience without risking a screw up at their hands -- which is really a screw up at MY hands if you think about it.

Great trick to do as a switch out after you've done some "regular" miracles. Hope this helps.

In lieu of having someone shuffle the cards you can have them spread the cards on the table and mix them up that way. The cards are never lifted off the table with this method and the spectator feels more directly involved. Especially when they push all the cards together in a single pile. They can palpably feel that this deck has been competely disarranged.

Just another option.