They can float as necessary with virtually no force needed. But once they encounter the boundary of their travel, ZERO movement beyond that edge is possible. On the picture above, there's actually movement possible in the radial and axial planes. When cold you can hold the disc and wiggle it around and it feels like there's nothing holding it on at all. Once it's warmed up, the radial play disappears, but the axial-play is still there to allow for self-centering between the pads.
If you're talking about bicycle brakes squealing, they have a long way to go in development. They're actually backwards right now. The early motorycle brakes had rigidly attached discs with floating calipers. That doesn't work anywhere nearly as well and as quietly as a rigidly bolted down caliper with floating disc.
Last edited by DannoXYZ; 10-19-08 at 03:16 PM.