Some of the newer machines can be pretty well fried by putting a magnet too close to their electronic parts, if you didn't mind gumming up the outside with adhesive. Mom's old Kenmore, on the other hand, probably has enough metal to make a new car, and could handle having a magnet stuck to it. Just be careful with the magnets, even the big ones they use for holding pins.
I have a pincushion that I was given as a gift, it is a goat. Super cute!
I'd check the web for fun patterns. I have seen a bunch of them.