Well Steve, you know my answer already, don't you?!
I leave everything on automatic and correct any things I don't like later in CaptureNX. This way I never
bother about WB. Shooting in RAW is helpful but not necessary in this respect.
: Most of the time I'm quite content with what the D80 (and I assume that the D40 has the same WB-strategy) produces. The times where I change the color-balance / grey-point would not have normally impressed my eye before I saw the result. Meaning: The eye is not the best receptor to decide what the color-temp is. And at the end I'd like to let a little of the color-mood of the shot seep through to final picture.
The cases where I correct is mostly when the important object is in the shadow of a brightly lit day. When you shoot a pic with bright sunny parts in it, the cam tends to use them as a reference for WB and the objects in the shadow tend to come out quite blueish. That seems to be a standard situation, but honestly, to give you advice here would mean to make a series of test shots with a deminishing portion of bright sunny parts to find out when the auto-WB tends to recognise the shadowy segments...
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