The "Sleep" function available to OS X users is a helpful preference to enable...you can walk away from your machine and know it will switch over to a screensaver or power down to standby mode. The Achille's heel is occasionally your machine will go beddy-bye when you're actually still there (while reading a long article, in the process of doing your taxes, etc). Should I Sleep, a will cure your Mac's case of narcolepsy by keeping an eye out for you...
The secret in Should I Sleep's ($1.99) ability to determine whether you're there or not there is accomplished by calling upon the aid of your MacBook or iMac's built-in camera. When installed, the app will turn on the camera and "look" for a user's face; if nobody is there, the machine will go into sleep mode as usual. If a face is detected, Should I Sleep prevents sleep mode, allowing you to continue reading, working nearby, or whatever you're busy doing. If you ask me, this should be a built-in option with the operating system.
- sleep machine will go to sleep only (saves state in RAM only, battery keeps RAM contents).
- hibernate only machine will go to hibernate only. (saves state on disk, battery will not be used).
- sleep and hibernate machine sleeps and hibernates. (default).
(Images: as linked above)