Apple has posted its Sleep Memory Extension file, set to eliminate a potentially data-destroying bug in Apple's system software.
We reported the problem on March 13 (see iBook memory trouble).
The bug can prevent your computer from waking up from sleep, and potentially affects iBooks and FireWire PowerBooks. A note on Apple's Technical Information Library (TIL) says: "Though you will most likely never encounter this bug, we still recommend that all iBook and new PowerBook (FireWire) owners download and install the following Sleep Memory Extension software patch which eliminates this bug."
After the bug-fix is installed, the "Preserve memory contents on sleep" checkbox will continue to appear in the Energy Saver control panel, but the option will be dimmed and unavailable. This also means the potential problem is solved. Download the fix from Apple's TIL site.