No, I never show my cards before putting them back in the deck.
I agree that sometimes that can be a good tactic. Showing your cards to an opponent, after you have successfully bluffed him, can sometimes provoke the opponent and affect his further game against you. But there is no guarantee that this move will successfully provoke the opponent, but it will definitely let the opponent know which cards you had. If you do it consistently, the opponent can conclude a lot about your game style.
Usually I don't think about that particular mind game at all, I rather don't show my cards to an opponent then leave him no doubt about what cards I had.