While I don't have magnetic implants, I have been wearing a magnetic ring the last few months. Much less intense, but something that is easily reversible. Finding fields has been interesting and when I do run across them I do stop in my tracks and move around finding the intensity/size of the field. Guess I could say it is like if you are blind and feeling a ball in the air. After just a few swipes through it and your mind can picture where the field is strong enough to "touch" and typically where the center is. Now with a ring I feel _way_ less than implants or other solutions and no doubt miss many fields, but it is still cool, fun, and simple (no batteries, surgery, etc).
It also has perks such as picking up small screws I drop, turning on/off my ipad/macbook/blackberry with just a swipe of my hand and dangling my keys if I need to hold something else in my hand.