David Williams (placed second in the 2004 main event) has a great article in the July edition of All In magazine entitled "No Mucking Way."
It is basically information on his style of play and how he seldom shows cards. Seldom doesn't mean never. He gives some specific examples of where he does show cards and how it has worked to his advantage. I tend to not completely agree with some of his article, but he is a pro, and I'm not. One thing he said he does, is when someone lays down a hand, and asks what he has, he may show them the less significant card of the two, like a 3. Leaving the guy thinking, "He raised me with a THREE in his hand?" That example seems like a great way to needle someone without giving away too much. You may have the hand beat or be on a strong draw with a lot of outs and still leave the guy wondering what the hell happened.
One specific example he gave was from the WPT World Championship at the Bellagio. He raised with a 10-7 in early position in an attempt to represent a big hand. The board came K-9-7 giving him bottom pair. He bet out on the pot and got one caller. The turn came A, and this time he bet out again, even bigger. Again, he was called. The river came with a 7 giving him trips, and he bet out even bigger this final round because he had the trips and figured they were good. On this street the other guy folded and Williams showed him the 10. For several minutes he said he could just see the guy wondering what the hell he had. Did he have pocket 10's and jam the pot on every street with a K and an A on the board? Did he have A-10, and if so how did he bet that 3 times into a board of K-9-7? He said the guy just stared at the board, stumped, wondering what the hell he had and how he bet it.
In this instance, I can totally see how showing cards or a card completely did the opposite of give information. He actually confused this guy more by showing him a card than by not showing anything. Had he not shown the guy would have most likely put him on AA, KK, or AK. Instead, the guy was completely stumped.
Having said that, I can count on both hands how many times I have showed cards, but with strategy like that, it makes sense to perform a little misdirection every once in a while.