Pretty much every singer has used some variation of a pitch-correcter at some point in their career. Utada included.

I know for a fact part of album version of B&C is auto-tuned (as stated on the Wiki page)
I also think "Let Me Give You My Love", "Wonder 'Bout" and to some extent, "Exodus '04" used some pitch-altering software, as those tracks were mixed and produced in collaboration with Timbaland, and he's notorious for pitch-altering pretty much every song he works on.

I also think given the mainstream producers for This Is the One, that auto-tune creeped in a little there. But who knows? As someone else posted, it's best to ask Utada herself.

Although I am almost 100% positive that Utada has only ever used autotune / pitch-correctors purely for artistic effect, and not to make her voice be carried through the music (unlike some other mainstream artists out there).

I don't know if any of this has been said before, as I'n too tired to drift through 5 pages of discussion (sorry!)