The real reason the Nine of Diamonds is rarely chosen is that it's the very bottom card of both the Aronson stack and the Tamariz stack.And no one is ever without one of those decks . . .
A favorite trick of mine, which I've mentioned before somewhere here on Genii, is Barrie Richardson's Any Card at Any Number. I use the Tamariz stack (sorry, Simon...) and have, as far as I recall, NEVER had anyone select the 9D. And I don't "force away" from it, as Barrie suggests in his instructions.
It's very interesting to me to note that Simon's stack also ends in 9D.