I think it was a penalty try personally. Even with Cronk holding him back for a good 5 metres Carney was still only beaten to the ball by inches. To me that means on the balance of probabilities he would have got there, and thats all thats required to give a penalty try.
Too many league people have it in their head that a penalty try can't be given unless a player has ball in hand and gets karate kicked in the head or something. Take a look at the penalty try given in the 2008 World Cup final as a good example of why last night should have also been a penalty try.
HOWEVER, I think the penalty try and sin binning rules need to be changed so that either a penalty try being awarded still results in the offending player being binned, or that a try scored while a player is in the bin results in that player being immediately allowed to return to play. It makes no sense that a penalty try being awarded negates a professional foul.