Evangeline Lilly:

~Evangeline(about a Jack & Kate romance): It will happen. Just wait for it - it will happen.
~Evangeline:I feel like she’s getting there, though. You can see the changes in Kate and you can see her growing and developing a confidence around Jack that basically has gotten to a level where she’s saying ‘You know what, you are just as screwed up as I am, and who are you to be above me?’ and I think once they get past that, it could be really amazing.
~Evangeline: I think, romantically, her heart’s more with Jack.

The writers:

~ Damon Lindelof:But then the more time spent on the island, the more Jack would sort of represent to Kate what she would want--stability and comfort and a real adult love, as opposed to that kind of lusty, frothy, "make out in the middle of a torture session" kind of thing.
~Damon Lindelof:On the other hand, Jack and Kate are a classical and romantic couple. They are amazed by each other, and as the time runs, they start to depend of each other, care about each other, the connection between them is getting stronger this season. There is always something, someone in their way. That makes the audience support them all the time"
~JJ"You could put, Jack and Kate on a, NYC street, and have them pass each other, at rush hour, on a Wednesday morning. And, they would stop, and turn, slowing to watch each other go by. They know each other within the context, of a universal recognition. They have met before, this life. And, they will meet again, in another."

LOST cast:

~Josh"Jack’s a keeper, and Sawyer’s a fun weekend."
~Josh"I loved Jack and Kate’s kiss. They really captured that moment, how it should be. And, that’s tricky."

Media:

~Kristin Vietch on Kate's 'choice' in season 3 "As far as “choices” go, I’d say, a passionate presumed pre-death romp, is not exactly proof, that you’ve, found your soul mate."