Chris Meyer posted the 10th of the 12-part series Deeper Modes of Expression, based on an extra in Creating Motion Graphics with After Effects, which was recently updated for CS5.
The 10th installment is Deeper Modes of Expression, Part 10: Random Numbers on how to gain finer control over randomness:
"Last month, I discussed using the wonderful wiggle expression to add randomization to your animations. However, wiggle is but one specialized application of random number generation. For those who like take the lid off and truly get under the hood, After Effects also includes the methods random,gaussRandom, and noise. In this installment I’ll also discuss changing random seed values (patterns of randomness), and how to freeze randomness in its tracks."