Behavior predicting can be surprisingly easy. Its eerie, are we leading a pre-defined life!? Ok, I can reason out the science of probability and all, but still , to be able to predict correctly 90% of the time what you will eat by what car you drive in to the restaurant, is completely surprising!!
Read about this amazing predicting system at : Hyperactive Bob
Amazon with its wealth of customer buying information can go to greater length in predicting your complete online behavior without touching any privacy concerns. Read the Amazon story at New Scientist