Speaking of power usage, there are two nice apps to help monitor battery usage in OS X. CoconutBattery is mostly useful for checking the health of the battery.

 

MiniBatteryLogger is a more advanced tool that monitors power consumption and levels over time. You can use it to see how particular configurations are consuming power.

Another, slightly related app is fseventer. fseventer shows filesystem access in real time and provides nice insight into what apps are using the hard drive.