That was my biggest problem with the film: Two pirate lords from the area, let alone ship, without letting us in on the circumstances allowing them both to have a piece of eight. I understand Jack Sparrow having a piece, it was handed down with his ship, but for Barbossa, who was there to pass it down to him? Is it something that can legitimately be stolen to count as "passed down?" We don't know, and we won't know.
Anyways, I walked into the second and third movie of the series with no expectations, mostly because I could barely remember the first movie for some reason. I thought the second movie was alright, but not an excellent film overall. I thought the third was actually pretty good, and received some unfair criticism, probably because of the success of the original film. I believe several websites were giving it somewhere around a 6/10, but I felt it was closer to 7.5/10. I was tired of reading reviews that complained too much about too double crossing in a pirate film. That's half of what the movies have been about, and I appreciated that the first thing that happened once everyone was in the normal world was a stand-off, as well as all the other tricks. People don't become pirates for the relationships, they do it for their own greed, excepting our two protagonists, Orlando Bloom and Keira Knightley, who character-wise, have learned how to deal with pirates by now, so they blend in as well as the other pirate main characters, when it comes to double crossing, though they try to do it for the good of others, and not for their own gain.
I liked the scenes where Jack was talking to himself. People I talked to said they didn't understand why the movie had those, but to me, it seemed to answer the question of whether he was crazy, or if he has everything planned all along. The answer being that he really is insane, and these other personalities basically influence everything he does, for the better. But that's just my impression.
The whole Calypso and Davey Jones subplot was a little gratuitous, though, and I think if they had either solidified it or just taken it out, it would helped the movie out quite a bit.