While I do have concerns that my OCs (who have a tendency to shack up with hot males) are a bit Mary Sueish, fortunately, I know the difference between a character created to be an idealised version of me, and a character created because my imagination wouldn't shut the hell up.
Take... oooooh... Hotwire. Gets shacked up with Barricade. That's a problem, I won't deny. But at least she doesn't change him. He's still Barricade. A Decepticon. A fractious bastard. Otherwise he wouldn't be attractive if I were emotionally diseased, and I wouldn't have a door poster of the Bad Cop on my door.
Also, nobody's being taken away from him. I dislike stealing people from people who are already shacked up.
Oh yes, and I don't think Litmus Tests are much use. After all, one of the early questions is "Is your character the same gender as you?" Well really. There's only two genders to pick from anyway, and there's a 50% chance it will or will not be you. And if it is the same gender as you, why's that such a sure thing for a Sue? Now if it's deliberate, maybe, but if not, you just got a point, biatch!