Out of curiosity, I had a look in Yoav Ben-Dov's 'The Open Reading' to see what he has to say about the Knight of Coins:
'Advancing toward a goal that seems close at hand but somehow eludes our grasp. ...Constantly chasing after money, either due to a real need or because in this frame of mind one can never have enough.'
Now that is not an interpretation I have ever used for Knight of Pentacles, though of course in the Rider Waite Smith deck, the Knight is holding the pentacle, whereas in the Tarot de Marseilles, the giant coin float in the air in front of his face, which could, I suppose, lead to this alternate meaning.
Well, I'm certainly not chasing after money. And in my tarot world, the Knight of Pentacles is the firm, stable, slow-going, patient, hardworking, gentle-spirited, self-effacing one in the tarot courts. Sitting firmly on his big, sturdy horse, well-rooted to the fertile earth, the sky awash with the glow of the life-giving sun, and bunches of lush greenery decorating himself and his horse's harness. I don't think he's materialistic, I think he's grounded, and those are not even close to the same thing.