Quick Brushes are a great addition to Aperture 3. They are located in the Adjustments popup menu, inside the Adjustments tab. Quick Brushes are exactly that, when you want to make a specific adjustment... quickly!
Some of my favorites include: Skin Smoothing, Polarize, Sharpen, and Definition. Being able to apply these types of adjustments to a specific area of the image without having to worry about creating masks is a wonderful enhancement to the post production workflow.
In this 7-minute video, I walk you through a typical Quick Brush scenario. You can see a larger version of the movie (better for this type of tutorial) by clicking through to YouTube or going to the Lynda.com Podcast page.
More Aperture Tips and Techniques
To learn more about Aperture 3, check out my Aperture 3 Essential Training on Lynda.com. Also, take a look at our Aperture 3 Learning Center. Tons of free content about how to get the most out of Aperture.