Here's a very quick video with two tricks for using the Curves adjustment tool in Aperture.
The first shows you how to use the curves to view an extended range histogram. One of the great things about the curves adjustment is that you can use it to show a full 32bit histogram, so even if you have no need to actually make a curves adjustment, you can use the tool to see the data that exists in your image file that is currently clipped at 100% white
The second shows you how to get better control when manipulating the actual curve. By using a few extra control points this tip shows you how to manipulate one part of the curve without affecting the other.