It is definitely not negligible. Slow playing is a valid strategy even against great players. If all but the top 5 hands or so fold every time you slow play, you're not playing against good players (experienced != good when it comes to poker) and you should just start slow playing and stealing every pot. Then when they figure it out, don't do it again until you get a monster. Most of abusing amateurs is simply doing this, exploiting a weakness until they realize it, then doing the opposite. By the time it stops working you're ready to go.

Regardless, presumably you'd have to memorize this order of the deck in order to stack it that way, thus you could look at your hand and determine the opponent's hand and what the board would be. You could play accordingly. It's easy to make a lot of money at poker when you know what all the cards are.

On the other hand, I've never seen a game for significant stakes where the players were dealt, and I've sure never known anyone good enough to take a deck and sort it into a specific 52 card pattern without being noticed.