Photoshop - Vibrance vs. Saturation

 
Let's take a look at the difference between vibrance and saturation using one of my favorite photographs of my adopted son all ready for prom.
Both tools are made to add more color to a photograph which can really make it pop. Unless of course you overdo and suddenly the photograph doesn't even look real any more.
The main difference between vibrance and saturation is that vibrance works to AVOID skin tones which are typically yellow and orange.
See how vibrance added more blue and green but didn't blow out the skin tones? Vibrance is usually the safest bet but when it comes to adding color to a photograph when you have people in it.
In photographs with people or a lot of yellow, you'll want to use vibrance to keep the skin tones looking natural and keep the yellow in check.

Here is another one of my examples about vibrance.
http://leonaruth.blogspot.com/2011/06/photoshop-magic-of-vibrance.html