The opportunity to see a hole-card is one of the most advantageous situations an AP can find. Because blackjack is so abundant, it is usually the first game that is considered when an AP scouts a casino. In blackjack, the edge can get over 10% by hole-carding. But that's a small edge by comparison with the edge obtainable by seeing the hole-card in some proprietary games.
The opportunity to hole-card proprietary games is much more common than blackjack. Poor training of the dealers, supervisors who don't take the games seriously and low house limits all lead to complacent security. However, there is a more substantial reason these opportunities abound: the Ace Shuffler. In addition to having a cradle that is 3 inches above the layout, many casinos place obstructions in the way. The result is a configuration that makes it nearly impossible for the dealer to properly and quickly bring the cards to the felt.
If you see a horror like this in your casino, do something about it.