Hibernation mode lets you stop your portable Mac from using any battery power while you aren’t using it, while retaining most of the convenience regular sleep mode. Even though your Mac powers off during hibernation, all of your open windows and applications are written to disk when it does—and then restored when you turn it back on. All Mac laptops since the release of the PowerBook G4 (including all MacBook models) ship with a hibernation feature, but it is disabled by default.
Luckily, there are several third-party applications that you can use to enable hibernation mode. Depending on how the speed and amount of flexibility you want, one of the following tools will probably suit your needs:
Deep Sleep shows up as a moon-shaped widget in your dashboard. You can configure the sleep mode that your Mac will enter when you click it, and the the sleep mode that your Mac will enter when you put it to sleep normally. (Note that the widget uses the term “Deep Sleep” instead of “hibernation”.)
SmartSleep adds an extra pane to System Preferences under the “Other” catagory when installed. It allows you to set the mode that your Mac enters every time you put it to sleep. It also includes an extra “smart sleep” mode which will automatically choose choose a sleep mode depending on your battery level.
Hibernation Tool is a minimal Applescript-based application with no options. Run it from the Finder or Dock, then click “OK” to enter hibernation. Most of the time it’s all I need to quickly go into hibernation mode.