I have to agree with most that the number of yellows this World Cup is on the high side, but ofcourse it is as a result of FIFA instuctions to referees to clamp down on things. That being said, the referee really has to use his judgement to make calls that are not to the detriment of the flow of the game.
I have found on several occasions that the refs have flung out that yellow card like a trigger happy soldier.
Cases in point, in the Sweden game when Shaka was taking a little long with the goal kicks, the ref went up to him and gave him a warning on what he viewed as time wasting but no card. In the game against England, the ref produced a card in one shot, no warning.
Argentina vs. the Serbs, the ref gave Crespo a yellow card for carrying on play after the whistle had gone for an off-side. Crespo claimed he did not hear the whistle. Ok so judgement call here, would a warning not have sufficed?
Lastly in another game (can't remember which) Team A got a freekick and a member from Team B was trotting back. Freekick was taken and it so happen to hit the player from Team B as he was moving back, bram, he get a card for delay of game
What I do agree with though is the cards for tackles, but again with judgement. While there has been embellishment by players on the receiving end (Sweden man vs. Avery) I have seen that players have been very clumsy with tackles and fully deserved a booking.