For some reason, the new iMacs have a limit as to how low you can adjust the screen brightness. If you like to work at night, or just in the dark, you'll probably find that the lowest screen brightness setting is not low enough. If you want to get better control of your screen brightness, checkout this program for the Mac by Splasm. It gives you more control over your screen brightness allowing you to adjust it down to very low levels. An additional feature of this which is nice is that as the screen brightness is reduced, they automaticall adjust the screen brightness and colors so that your screen does not get washed out.