Hi Sarah. I was making a small tut to answer Emily, and add to yours. While you were answering the question. I hope you don't mine if I posted anyway.
after all it's for the benefit of all our sisters and brothers in arms
Ok first, understand two things. Photoshop is filled with Idiot buttons ( Now before you call me mean ). Let me expand, Idiot buttons are what I call presets (yes I use them too. If they work.). For example sharpen and more sharpen are presets based on the Unsharp Mask tool. Their just some ones settings that work well for a a lot of cases. The Second thing is simply this.... Unsharp Mask means ADJUSTABLE SHARPENING.
So here we go. Understanding unsharp mask. What this tool is doing, is adding white dots and black dots around the colored dots of the original image. That is why it is so important that is the very last step and it is used only once.
Hope this helps
Scott