>Just to clarify what has already been stated. The meter will >give you an idea of the exposure before you take the shot. The >histogram will tell you the exposure after the fact. You can >then make adjustments in the next shot.
As already mentioned, the histogram is not really meant for exposure evaluation. It is just a graphic representation of the distribution of pixels based upon tonality.
>To Eric's point about camera settings and the histogram. Is >this a subtlety or is this measurable in stops?
For me there is really no one correct answer to this question. How much the histogram will shift depends on the amount of variation due to the settings. As Eric eluded, a high amount of saturation and sharpening can cause clipping. Keep in mind there is a distinct difference between clipping due to settings and sensor site saturation due to overexposure. That's why I feel saying that you can recover lossed highlights can be somewhat misleading.
It really depends on your shooting style. If you're a get it right in camera JPEG shooter, then chimping to alter exposure using the histogram and blinkies screen might be desirable. But that can actually lead to under-exposure in the right conditions. If you want to squeeze every ounce of performance out of the sensor yet still chimp, then setting Picture Control to neutral with no sharpening and a bit of reduced contrast would be desirable.
To me, rather than depending upon the histogram to set exposure, it's best to learn how the metering system functions in the different modes and learn how to use it depending upon the scene conditions and DNR.