[Fast Corners]

Check the alignment of the front end. Even with a bump steer adjusted for a lowered car you can have the car pull left or right and back again during braking. If the surface is bumpy or irregular and you have very little toe the car can feel unstable. Flexing in the suspension bushings can cause changes in toe setting that may push you to a slightly toe out condition.

I would check your toe, caster and camber settings to see if they are in spec and I would also check the condition of the front suspension bushings. If the shocks have 90K on them then I would imagine that the bushings would have atleast that kind of mileage on them.

In reading you post again, I noticed that it varies based upon the road surface. This leads me to believe that it is the front end alignment or bad bushings. If your rotors were the culpret it wouldn't make any difference on what the road surface was like. Additionally, with a lot of neg camber you are reducing the contact patch when going straight. This can have significant affect on braking on a bumpy surface. With smaller contact patches it is easier for the tire to be unloaded when it goes over a bump. In effect a momentary loss of traction on one side will cause the car to pull to the side which does have traction. When the tire regains traction it will tend to pull the car back that direction.

How stiff is the car sprung? What shocks are you running?