Hi folks,
It is possible to make money by card-counting in Blackjack. In fact, a good friend of mine has spent years doing it in casinos in Las Vegas, where he lives.
Unfortunately card-counting doesn’t work at online casinos because they shuffle the deck constantly, so don't even try it.
Over recent years, land-based Casinos have made it more for difficult for card-counters to gain an advantage. Casinos now put more decks in the shoe (typically six decks per shoe in Vegas casinos) and also shuffle more often. The shoe is the term for the box holding the decks of cards, the cards are dealt from the shoe. The card-counting advantage becomes higher the more cards that have been dealt, referred to as 'penetration' of the deck/shoe. Shuffling cancels your edge. To be most effective, you need penetration deep into shoe.
Methods of card counting are actually incredibly easy to perform. A common technique simply invovles keeping a running total in your head, and simply adding 1 when low cards are dealt, or subtracting 1 when high cards are dealt. The size of the running total then enables you to judge whether the remaining cards in the deck are likely to be predominantly high value cards or low value cards. Then you can play your hands with that knowledge.
Plenty more details are given here on wikipedia:
http://en.wikipedia.org/wiki/Card_counting
Cheers,
Gavin