I agree that Chow Yun-Fat's character only seemed to be in the movie to advance the plot.
Spoiler Below And once they were done with him, they killed him.
BTW, what did everybody think about Keith Richards', much hyped, cameo?
EDIT:
Here's my thoughts on the cameo:
Spoiler Below It seems that in order to fit the character of Jack Sparrow's father into the story, they just took the "Keeper of the Code," which could have been anybody, and added a few lines to him referencing him as Jack's father.
It was good though.