As for the WD model mentioned in my last post, colleagues who use it for critical business backups (on multiple Macs, using Time Machine) tell me that it does the job right out of the box (ie, they've never had to reformat the drive prior to use).
The reason for that, I just noticed (Pogue, p 262), is that "Time Machine automatically reformats [drives] to the Mac OS Extended (Journaled) scheme, which it requires."
