The relationship preferences that a lot of Lost fans seem to be so passionate about don't seem to interest me for some reason. Lost relationships have caused a lot of contention in online wars between the Jaters and the Skaters (and now Juliet is thrown into the mix!), but I don't care so much. I admit that I was happy for Hurley when he and Libby were getting together, because it's always great when the nice guy gets a break in a story. I also prefer to see married people like Sun and Jin stay together, and for new families to begin like with Charlie, Claire, and Aaron. Of course the depth of interaction, conflict or otherwise, between the characters in any story are very important. But so far I haven't emotionally invested any preference of whether Kate chooses to be with Smokey or anyone else on the island.
At this point, Kate and Sawyer have physically and emotionally gone light years beyond where Kate and Jack are, for the obvious reasons. And Jack seemed to have been resigned to leaving them to be together after he "accidentally" viewed their sleepover in the cage. But then Moses goes and tells Kate that he loves her on their flight through the wilderness in the finale! That's nice Jack, but it may be too little too late.
Personally, I don't think that Jack knows what love really is. It appears that Jack mistakes love for whatever surge of emotion that he feels for the "needy damsel du jour", which viewers have discussed in detail since seeing his FBs. Though like I've said before, Jack could possibly lift Kate up from where she holds herself down, but does Jack really know Kate anymore than Kevin? Accept for the fact that he learned she was a fugitive, he knows nothing about her life. Sawyer knows her better, even just from playing that "I Never" game with her. But Sawyer drags around his own baggage of moral and personal issues too.
Even if Juliet does not inevitably draw Jack away from Kate, I think that Kate should try to stick it out with Sawyer, since she made the choice to get physical and bond with him (repeatedly!). We would hate to see Sawyer find yet another reason to crawl back into his pitiful crusty shell. Who knows, maybe by the end of the show it might just be very important to the story who Kate ends up with. But however TPTB write it up is OK with me. I'm sure that they will make it a compelling component to the story whichever direction that Kate turns.