> But realistically, if you really want to do power management on any sort
> of disk drive you should have backups/mirroring and be prepared to replace
> it after a while.

This is much more true for desktop drives than for laptop drives.  Modern 
laptop drives are designed for many spin up/down cycles.  They actually last 
longer if they're spun up, used, then spun down than if they're left spinning 
all the time.  See, e.g., the IBM specs for details.

	--Ed