"Promise is a promise!"
Best line of the episode, by far.
Ben, probly already knows that Sun blames him and is plotting with Widmore so now that Locke just gave him his get-out-of-jail-free card with her and knowing that he's going to kill him, eventually, Ben gives Locke the most spectacularly insincere pep talk response of the modern era.
Great line. Well delivered. Even the Romanian judges give Emerson a 10.0.!!!