Originally posted by Alex:[..]
Supposedly it depends on the stuff that the pickup covers are made of. German Silver (which doesn't actiually contain any silver) is supposed to be the best metal for pickup covers since it's said not to influence the sound. Cheaper metal is said to cut highs, making the pickups sound muffled. But I haven't A/B-ed it. I bet on quality pickups it's nothing more than just a different look.
Alex
I think that even on the good ones it makes some difference...just look how Jimmy Page was always changing the pick ups on his le paul from covered to uncovered.