Magnetism, how does it work?
Miracles.
Seriously though, I think Magnetism in combat is misunderstood right now. I'm fairly certain it's not going to be a "Homing attack" like many people are assuming. I just think, in battles where there are allies an enemies (Since we now know Companions are going to be more common), if your companion or ally happens to get "Near" your target, as is very common in melee, the game's combat will never strike the ally as long as their "Hit box" occupies the same space as a hostile target.
So the only real way you'll notice it, is if in a battle, you decide to intentionally attack your ally. If he's too close (IE right next to) the combat engine will register your weapon colliding with the original hostile target instead.
That's how I interpret it anyway. I'm pretty sure if it was Auto-sighting, it'd be called auto-sighting.