White balance is really critical, and I wish I had known this a long time ago. When I bought my camera to go to Kenya, I knew even less about photography than I know today—hard to believe, but true. It turns out that the weather was mainly overcast, and this led to pretty drab photos that I wanted to touch up later. As it happens, automatic color adjustments in most software programs are not really all that great: they overcompensate based on slavish adherence to the color or value curves in the image histogram (this doesn't really need to mean anything to you at the moment, but it does give me an idea for another posting sometime). This is okay when colors are normally distributed in the image, but usually they aren't—that's why we want to fix them in the first place.
The drabness of an image is often the result of improper white balancing. A warmer white balance leads to more saturated photos with deeper reds. In shady conditions, this is usually needed to counteract the bluer tones in the scene. Ken Rockwell (linked right) has
a good article on white balance that's worth a quick read, and others exist on the web, too.
This is a bit of an article on my experience.