I had my rotors replaced (third set for this car, but first under my ownership) in the fall and have noticed the brake vibration comes and go. If I use brake cleaner and scrub the rotors, and then do some hard braking, it dramatically improves. I really believe it's a behavior of the brake pads. When I go out and actually drive the car hard and burn up the brakes (I get on a back road and brake from 60-25 a few times) it improves. For me it's most noticeable vibration around 35 mph when "trail" braking. At any speed if I hit the brakes hard they immediately bite and I lose vibration. I've changed the way I brake to a bit more "harder pulse" style and it seems to help. It's definitely annoying and I'd like to try some of the other lower dust pads to see if it helps.
If anybody has any experience with those pads I'd love info.