Catastrophic Apple Data Loss A Feature Not A Bug
To be fair to Apple, it does warn users not to move the machine until this process is complete - at which point the light on the lid catch begins to pulsate - but it's easy for users to grab their laptops and go as soon as the lid's down.
Unfortunately, at that point, the drive's heads may by busily moving back and forth across the platters, and any movement risks the two physically touching, with the potential of data loss and even disc damage of the kind described by Retrodata. This is true of all hard disks, as proponents of solid-state storage like to point out.
It would seem wise for all Apple users to disable the Safe Sleep feature as this is the likeliest culprit. The advice in the Apple forums that it's your fault for moving a laptop or Seagate's fault for selling their hard-drives to Apple is probably not going to help you when your precious data is ground into metal shavings.