I dont' know if this has been said but...
Lets consider that someone is looking at their cards like what was mentioned above, so that the person on their left and right can see what they have. You're not in either of those positions, so you're not cheating by looking, and you're not the dummy showing off the cards that easily, but you're the sucker who doesn't know what 2 other cards are already out of the deck. If the guy to his left has A10 suited in spades, and sees the guy to his right is holding KQ of spades, he knows he only has 9 cards left that can make his flush. Or if that board hits KKA, he knows the chances you have that King are pretty low.
I'd say that there should be some sort of rule that picking up your cards and looking at them in a way that is so easily seen by people on your left and/or right is illegal in some way, or the dealer should reprimand the guy. I don't want my opponents having a bigger edge about what cards are left.
just my (uninformed) 2 cents