I gave up using Bridge years ago. It seems to bog computers down.

I became used to viewing in Faststone and opening into ACR from there, simply by pressing the "E" key in Faststone. Then I discovered the custom Picture Settings I run in my Canon camera settings, were not being carried through to ACR, then into Photoshop (CS 5.1). That was a bit of a pain, so I revisited Canon DPP. That worked out much better. My Faststone is set to automatically open Canon raw images into DPP with the command Alt + 2, and from DPP into photoshop with the comand Alt + P. The images come into Photoshop as a .tiff, and with my custom Picture settings intact. I do feel the raw images are better converted by DPP than ACR.

I think Arthur is thinking along good lines. Even though you cannot see the editing changes in Bridge, are they being saved with the image? When you reopen the image in ACR, are all your original edits intact? If they are, I'd probably look at Bridge causing the problems.

I just opened Bridge CS5.1 and opened a canon raw image into ACR. I edited the image and clicked Done, just as you have been doing. Back in Bridge, my image is not refreshing to the edit either. On playing around I managed to get the thumbnails to show the edited version by right clicking on the thumbnail and choosing "Generate High Quality Thumbnail".

If I right click again and this time choose "Generate quick thumbnail" the thumbnail remains showing the edits. This suggests it may be a thumbnail refreshing problem.. I have to go back to work now, but if there is time tomorrow, I'll investigate further.