After some discussion in another post, Myra said:
On a D80, you do this: Fit your white balance cap on the end of the lens. Then you set the white balance to "Pre" - stands for preset - using either the menu or by depressing the WB button and scrolling the back wheel. You depress the shutter half way while holding the white balance button in and on the top lcd screen you see the usual exposure and f/stop info and a flashing "PRE". Still keeping the shutter held half depressed, attach the white balance cap and fully depress to take a shot through the cap. If the shot is suitable, you will see "Good" come up in the top lcd screen. This then sets and stores the white balance for the particular light at that time. So all your subsequent shots for that particular lighting will theoretically be correct for white balance.
I'm assuming that you can do the same with either a white or a grey card, but a more knowledgeable person will have to come along and confirm/deny that.
Seems to me that by mastering this, you can save a lot of time in pp, as you don't have to correct a lot of dodgy white balance.
But you would have to remember to re-set the WB for each shooting session.
Please note that I haven't tested this yet, as it is night-time. But I'll have a go at this during the day tomorrow and get back.
I hope I have all this right and am quite happy to be corrected.