I don't let anyone touch my decks. I'm not as militant as that answer sounds up there.
People have touched them, it does happen from time to time - how can you say no to a friend who asks in a tiny scared voice: "May I pick the deck up, please?"
But I still cringe, when I see it. I think it's a form of germaphobia, though in a metaphysical sense. I don't like other peoples energy mixing with the connection I have established with the cards.
When my best friend cleanses them sometimes as a favor, I actually feel it in my palms.