I realize this is a redundant post - I want to make sure someone at Adobe notices. Adjustment brush previews are turning off when you hover the cursor over the edit pin, and stay off until off until you hover cursor over another pin. Neil Carboni took the time to make screen shots that show the problem. See previous post and my Windows 7 x64 specs at http://forums.adobe.com/thread/1083526?tstart=0
The Adjustment brush previews work as expected so long the Show Mask option is checked AND one of the of the Adjustment Brush pins is selected; so one mask is always showing.
For example, when a previously edited image is first re-opened in ACR, no brush pins are selected (Show Mask can be checked). If I hover my cursor over one of the pins (for example I have 6 brush adjustments) the mask flashes on for the associated edit, as expected. When I move the cursor away, the edit preview disappears as if the edit never happened, but the pin remains. I then select one of the pins by clicking on it to make that edit live. Now when I move my cursor over a pin the mask for that pin flashes on, when I move the cursor away from that pin the preview of the edit is showing. Now the preview works for any brush edit.
Makes working with multiple adjustment brushes extremely difficult - not always sure if the results of a previous edit are showing. Have to constantly move my cursor and hover it over another brush pin to verify that I am seeing results of previous edit. If the preview is not showing, as soon as I put down the brush on that edit, the preview springs to life. I do not see this problem using ACR 7.1 on my Vista x64 machine.
As my previous post indicates, I have updated the driver on my FirePro V4900, uninstalled and reinstalled Photoshop, etc. Did not see the problem after I reinstalled Photoshop and briefly used ACR 7. Problem came back once I updated.