Being a portrait photographer and a mostly environmental one at that, skin tones are very important to me. Most of the time I don't have complete control over the direction, intensity, and color of the light I use. It might be a tungsten bulb from the lamp next the guy in a room with florescents, and then I bring in a daylight balanced strobe to try to make something nice out of it. It's a nightmare in post to get all of those lights to merge. Usually involving multiple exports of the RAW file at different white balances, and then masking them together in Photoshop.
The thing is, being 'right' isn't always enough. Sure, I could use a gray card and eye-dropper to color correct, but it doesn't always work as well in reality as in theory. Sometimes neutral is a little TOO neutral. Or, just because you're outside in the afternoon doesn't mean that the daylight WB setting is right on, there is a fair amount of variation. For example, I think the cloudy setting on Canon camera's is way too warm, and auto WB sucks at tungsten lights which change temp over time.
And since different lights have different spectrums as well as different colors, you can't guarantee that you can get correct colors out of some lights, no matter how hard you try playing with white balance and tint. I tend to find this the most annoying when working with photos of people with pale skin, as the color is usually very subtle and difficult to capture.
There are people on both sides of the big camera debate that'll say that Nikon or Canon has better skin tones, or that to make it work you've got to use the manufacturers RAW converter because Adobe and Apple can only reverse engineer the curves and they only get it right some of the time, and not at all in others. I'm a Lightroom user, so the ACR engine is my tool of choice. With the release of Lightroom 2, Adobe installed custom camera profiles for Canon and Nikon models which simulate the look of the built in 'picture styles' and theoretically level the playing field between ACR and the manufacturer's software. I can't verify if that's the case since I don't even have the Canon stuff installed, but it seems people think it's about right.
I however, have not had the greatest luck with any of them. They're better than the adobe defaults from Lightroom 1 to be sure, but they're just averages of a few different examples of each camera that Adobe tested, not necessarily yours. So last night I was looking about on the net and found the DNG Profile editor that Adobe has released, which lets you create custom profiles for your camera. All you need is a Gretag-Macbeth Colorchecker (too expensive for what they are, but very handy to own) and a couple minutes of your time. Take a photo of the color checker in nice even light (I used a daylight-balanced profoto strobe), feed it into the editor and it'll create a custom profile based on YOUR camera. You then export it and it'll show up in Lightroom's Camera Calibration profiles list. It's early on, but so far I've been pleased with the colors it's giving me. Closer to what I want than the canned profiles, especially in the skin tones where it counts.
Here's a link to the editor: DNG Profile Editor
So give it a try yourself. Worth the few minutes if it'll make your color work that much better in the future.
Also, more questions from anyone that's got them. Would love to answer some more.