Avoid these like the plague...
...because they *are* a plague in nearly every way.
If you don't count the incredibly cheap and nasty construction of these things, there is the so-called SmartWare to contend with. That's the "plague" part. If you don't want it, you can't get rid of it. The USB-only versions of these drives have at least a firmware upgrade and utility tool available to hide (but not purge) the SmartWare "feature".
The Firewire/USB drives (like this one) have no such ability. Worse, the WD Tech Support web site did not used to say this, causing a frustrating situation. You're stuck with SmartWare forever, which wouldn't be so bad if it worked or did anything desireable at all. Truth be told, it's very buggy and unreliable for both Mac and PC.
Western Digital Technical support was less than useless and despite their promise that something would be coming along soon to address this, nothing has. That was in December of 2009.
I finally returned the drive and bought from the competition. It meant giving up Firewire, but to have a drive that was "simply un-fooled-around with" that was a small sacrifice. Too bad...I generally do prefer WD's drives, but if they can't even provide tools to remove SmartWare and behave in even a mildly competent manner, what *else* might they be doing badly or hiding?
Stay away from these. They're bad news in almost every way.