Casinos have a new tool to use against blackjack card-counters, as described in this Wired story. The tool is designed to help casinos calculate comps (compensation given to good repeat customers which keeps them coming back). However, it could easily be used to detect someone who varies his bets depending on whether the state of the deck favors the player or the house -- the basis of card counting.
It seems to me that blackjack is becoming more and more of a losing game. I've never played it for money myself. I just couldn't get into all the memorization. At least I have a shot at poker.