Twice now I have seen necklaces that purposely sit off to the side of the neckline. I don't remember where I saw the first one; the second was on the new WB show, "Hart of Dixie," via the character of Rachel Bilson. (On a separate note, I'm loving her wardrobe on that show, with all of the striped shirts, wonderful neutrals, and other gorgeous pieces.)
Anyway, I love the look of an off center charm, because I think it can add a little bit of whimsy and playfulness to a structured outfit. This style is definitley on my want list.