Now that's changed with the SmartSleep preference pane. It allows you to set all the possible settings plus a new one. From the preference pane itself:
- smart sleep: sleep if battery charge is above the sleep & hibernate level. Hibernates only when battery charge is below 5% or less than 5 minutes.
- sleep: machine will go to sleep only (saves state in RAM only, battery keeps RAM contents)
- sleep & hibernate: machine sleeps and hibernates. (default)
- hibernate only machine will go to hibernate only. (saves state on disk, battery will not be used)