What color space is Camera Raw set to use? What is your working space in Photoshop? Is your display calibrated to any degree?
ACR is set to use sRGB (but I've tried AdobeRGB with same results), Photoshop is also sRGB (just verified), monitor is an Apple Cinema Display using Apple's profile and it is dead on with my prints.
The very odd thing is that I can save a JPG, immediately open it and put it next to the ACR window and they are off.
Ok, check out this experiment I just did...open CR2 from Bridge into ACR (they look the same), save image as JPG and open in PS and place next to Bridge (they are different, PS is darker), open exact same JPG in Bridge and compare to CR2 and to CR2 in ACR and they are the same. So what is ACR and Bridge applying to the images that they are displaying where Photoshop and OSX Preview are not?