[fjtorres]

My (limited--two month) experience is that relying solely on the keyboard-lock time-out results in lower battery life than enabling auto shutdown and rebooting as needed. Given that the PB360 has a real-time clock that draws some current and it repaginates on the fly, I'm assuming there are some background processes running at all time. Even in the most power-hungry configuration: active accelerometer, long time-out settings, etc, I still got over a week of use, versus over two weeks with conservative settings. That's with an 8GB SDHC card in place full-time.
Given that boot time runs around 10 seconds I'm happy with auto shutdown enabled.
Your mileage may vary, of course.