If you have upgraded to Photoshop CS3 or CS4 or if use Lightroom, then you have encountered Vibrance. Consider it a smarter less heavy handed form of Saturation. Saturation will saturate all colors equally, and it is easy to go over the edge into blobs of frightening color and loss of detail in a color that was pretty saturated to start with, just to get the saturation up on another color that started out less saturated. Vibrance on the other hand will saturate less-saturated colors more than ones that are already more saturated. It will also protect somewhat against oversaturating skin tones. Consider this example. The first image is before adjustments. My goal is to increase the saturation of the colors in the hat.