I am by no means a photoshop guru but I learned a bunch of things at a workshop that I just attended. They encourage sharing the info so I will do my best to do that. I use CS4 and a Mac so my ramblings will be centered around those. This is actually the last thing that we learned so I'm a little out of order which is why I called it part 2
A very powerful yet simple tool that is available is the contrast mask:
In CS4, with an image open, open the Channels box. Command Click the RGB channel. This will load a contrast mask. It won't "do" anything obvious, yet. Now go to the layers box and while holding the Option key down select the create new fill or adjustment layer icon (black and white circle) with the mask that you just loaded from the Channels selection. Because you held the Option key down you also get to set the type of adjustment and the mode of the adjustment. Start with Curves and Normal. I also use Luminosity, Hue, and Saturation modes but for now start with that. Now you'll have an curves adjustment layer with mask. Option click the mask. The screen now displays the mask. With masks, the easiest thing to remember is that black takes away the effect and white makes the effect 100%. Varying shades of gray cause varying levels of the effect. Just for fun, while the mask is selected (in the layers pallet) hit Command I. That inverts the mask. Option click the mask again to go back to the normal image. Grab the curves line at about 50%. Pull it up and out to the upper left corner and watch the image. Now pull it down and out to the lower right corner and watch the image. Hit Command I while the mask is selected and do the same thing with the curve. Very quickly you can go from playing with the curve to balancing the image.
I "rescued" the image below using this technique. The sky was way too bright and the bird was lost in it. It's not something that I would print and it's not something that I am in love with. I shot it with this post in mind.
My first step was to drag the background to the Create a New Layer icon on the layers pallet. Then I changed the blend mode to screen. Blend modes rock btw. After that I adjusted the opacity (not much in this case) to try to balance the bird with the sky. Once that was done I flattened the image. Typically I wouldn't flatten but since this was just for web posting I flattened it. I forgot to mention that noise removal, spotting, etc are all done ahead of time. I actually try to do spot removal in ACR now. It seems to be faster and easier. Next I used the contrast mask (inverted if I remember correctly) to balance the image and give it some semblance of "pop" ("pop" in an image this washed out is an overstatement

)
This is a bad example of how to use a very powerful tool. It's not a "fix-it" tool. I used it that way... and I am demonstrating it that way... but that's not it's strongest point.
Before:
After:
