An Explanation of the Kiss and Flirtations of Jack and Elizabeth
Actually, the scenes were over acted by Kiera, and the compass was used incorrectly, but the intent of the writers is still clear, even in the script version where J/E is not so...in your face, as it were.
Basically, all the flirting, the teasing, led up to Elizabeth kissing Jack. The kiss is a necessary plot element in three main ways. First of all, it allows Elizabeth to use her knowledge of Jack's weakness and vulnerability about her against him. Second of all, it allows for Jack not really being able to make a choice about facing the Kraken so he can die, and third of all, it drives the plot in the third film by giving Will the incentive he needs to fully embrace his piratey side.
Without the flirting and teasing, there's no way that Jack would have allowed Elizabeth to kiss him without knowing that something was up. He was already suspicious enough while she was kissing him, even with all the flirting they'd done.
So why bother with all of this if J/E is not meant to happen? To make what happens with Will and Elizabeth all the more shocking -- not to YOU, since you like J/E and you're on a messageboard looking for spoilers, but for the general audience who doesn't go hunting down spoilers, and who doesn't pick apart scenes in a film, seeking clues.
What is going to happen for Will and Elizabeth really does surprise me, and I can only imagine the reaction of the audience who knows nothing about the plot. It's going to be good. I imagine there will be gasps, people really into it might say, "No!", there will be tears.
See, in Hollywood, the girl and the guy hook up after lots of Issues. After they get together, there is supposed to be a big kiss, and then a happily ever after.
You aren't supposed to have them get over their Issues, have their big kiss, and then have one of them fatally wounded and then become a captain who can only see his love once every ten years.
That's...not Hollywood. It's not Disney. There aren't supposed to be more Issues after the other ones have been wrapped up, unless you're in a horror film.
Good guys are supposed to win, bad guys are supposed to die, and everyone goes home happy. The whole reason they're trying to keep the ending from leaking out is so that the general public is SHOCKED, happy, crushed, and lastly, hopeful when they leave the theatre.