Chris and Trish Meyer posted the 9th of the 12-part series Deeper Modes of Expression, based on an extra in their book Creating Motion Graphics with After Effects, which was recently updated for CS5.
The 9th installment is Deeper Modes of Expression, Part 9: Wiggly World on "how to apply the basic wiggle expression, and then add finer degrees of control to it. ... We think the wiggle expression is one of the core tools to include in your expression toolkit. However, you should know that many basic wiggle moves are available as a set of Animation Presets (look in the Behaviors subcategory). If you want to dive even deeper into random values, the next installment is for you. In it we’ll discuss the differences between random, gaussRandom, and noise, changing seed values, and freezing animations. [emphasis added]"