[Kumabjorn]

Tough question. I would assume that an excellent caddie for someone like a DL3 is very different from the requirements of a Kevin Na. The experienced player may sometimes turn on autopilot (being nine strokes behind on Sunday morning and the card secured) and it would be the caddies job to get the player focused and excited, whereas a young rookie or sophmore might get overly excited (being two strokes behind on Sunday and watching the leaders hit a wild shot) and the caddie has to cool down the player.

I would probably summarize the requirement most sought after is a keen sense of responsibility, but I realize the content will differ from player to player.