The Adjustment Tool Guide gives an in-depth-view of the Adjustment tool in Aperture. The documentary provided by Apple isn't that what most people were looking for. But Kendall Gelner wrote his own Adjustment Tools Guide originally for the Aperture Version 1.0.1.
Now he has updated his excellent Guide to fit with the current Aperture Version 1.5.2. His new guide now has a cool visual walkthrough of the Edge Sharpen Tool introduced in Aperture 1.5. The Adjustment Tool Guide can be downloaded as a free download from Kendall's Aperture-Website (which was named Inside Aperture long before the well-known blog from o'reilly started):
Kendall also provides a so called Quick Reference Guide for Aperture which isn't updated yet and therefore only covers Aperture Version 1.0.1. Nevertheless, it's a good starting point for understanding the different little badges on your images in Aperture. Just the badges for referenced images aren't covered:
