phantom, I'd buy that if the center of mass wasn't firmly inside the earths surface. As such, the earth isn't even perturbed by 1 earth radii. Therefore I'd call it a moon.

If you call us a binary planet, what's to stop mars and it's moons being a trinary? or jupiter and its moons...

Now, if that center of mass was outside the earth...then I'd agree whole heartedly.