From: senrath
Counting cards does work. The only problem is that it isn't actually that profitable on your own, which is the only time it's legal.
It is not illegal by law, just by casinos. You cannot be fined for card counting because they cannot prove it. And plus, using your brain to do good in the game shouldn't be against the rules in my opinion :)
In black jack, if you follow the basic strategy card for all situations (google basic strategy card for black jack), the house has a 50.6% advantage and you have a 49.4% chance. So the house has an advantage of 1.2% without you counting cards.
If you count cards perfectly (which it probably gets hard to do it in casinos with all the noise and trying not to look like you're thinking too hard, you can't use your hands to make numbers…etc.) You can end up with a 3-5% advantage over the house.
With 1 deck you can REALLY increase your odds if you get a hot deck (which is more common in smaller decks). The problem is they keep a very close eye on 1 deck tables (if you can even find one) and the shoe is further up so less cards are delt (I think it's usually reshuffled every time with a lot of them).
Counting cards is easy. Count starts at 0. 2,3,4,5,6 = +1 to the count. 7,8,9 doesn't change the count. Everything else -1. That's for hi-lo counting system. There is also the KO system which I kind of like which calls 7's a good thing to get rid of. So 2,3,4,5,6,7 = +1 8 and 9 = 0 and others are -1. If you count a whole deck right using the KO system, you will not end up with 0 at the end like with hi-lo, you will end up with +4.