Mac OS X has some built in features to help you save energy. Not only does this help the environment, but it saves wear and tear on your mac & your wallet (electric bills!). I sit down at my Mac at 7:30AM every morning. So, instead of leaving my mac on all night, I have it wake itself up before I even arrive at my desk. I have it shutdown at 9PM in the evening too (that's where the energy savings comes in). Here is how to do it: Finder-> Apple menu -> System Preferences. Next, choose 'Energy Saver'. In the energy saver menu, make sure the 'padlock' is unlocked. If it isn't click on it, and authenticate with your Administrator password. Then click on 'Schedule'. Finally, setup your preferred 'wake up & sleep schedule', then click 'OK'. Your computer shuts down automatically at the scheduled time if you are logged in. If you are not logged in, your computer will not shut down at the scheduled time. Also, I recommend you leave your computer on overnight occasionally. Mac OS X is unix based, and it needs to run it's maintenance scripts during the night, to keep you mac running healthy. So, occasionally, disable the sleep/shutdown, and let your Mac stay on overnight (you can turn off the display though).