I know I'm way out from the median LJ user, so you'd be insane to design for my issues. The problem with designing from metrics is it can be very hard to correctly match the behavior seen in the metric to the real-world issue generating it (this is a large chunk of my day job). I push Cooper's book because it looks directly at how to design to the different types of human behavior by modeling with personas. If you've seen material on that technique already sorry to bother you with it.