In CS5, I see the brush softness indicator is now so tiny I can't see it change. In previous versions, as I used the shift/bracket keys to change softness, the little circle in the top bar would blur or return to a sharp edged circle for no softness. Now it is so small I can't see it change, and I have no indication of the status of my brush edges. We need to get a good indicator!
The behavior hasn't changed in CS5.
So I'm not sure what you are actually requesting here.
Are you using Open GL (Preferences > Performance)? If so, there is a better way to see how soft your brushes are.
If not, the preview top left of the options bar hasn't changed between CS4 or 5.