@ TB-AV : I've used fine steel wool (AKA 0# grade) plenty of times on pickups for local guitarists who didn't dig rust (which they get from time to time, living near the coast and all), if you use the fine grade there'll be no problem.
It's not as if the magnets in a pickup are so strong that the steel wool becomes this unremovable mess IF (and that is a big IF) any bits come off onto the pole pieces.
I'm also not suggesting the OP should go nuts on them, a slight rub is all that's needed if it bothers him.
And no, i will not smack myself with a trout, that would be severe animal cruelty, and since PETA already wants me dead for wearing leather boots and a leather jacket, the last thing i need is them breathing down my neck for abusing a fish

@ Borodog : agree with never ever using a magnet to remove bits of steel wool from the pickups, as it's just a bad idea, but i must partially disagree with 'demagnetizing the polepieces' bit, as that would depend on how the pickup is constructed.
See this image for example :
https://d2wvyzrb6llnwb.cloudfront.net/article_images/large/1118576_com_magnetswap.jpgHumbuckers (and quite a number of single coils these days) are constructed that way, the polepiece screws and slugs will simply be ferrous.
See also :
https://www.google.com/search?q=anatomy+of+a+humbucker&safe=off&source=lnms&sa=X&ei=QLPqU8eGGIniOs6TgKAG&ved=0CAcQ_AUoAA&biw=1920&bih=870&dpr=1And for sake of information, here's what a P90 looks like :
http://www.planetz.com/wp-content/uploads/2011/05/CoAxe-Bobbin-Assembly4.jpg@ shadow : for slight patina, yes, for actual rust, the microfiber cloth will not do much if you really want to get rid of it.