I've had exactly 4 Western Digital HD's fail on me & all of them were the same model-run of 120gb ATA-100's from maybe 3 years ago ... this makes them the second least reliable drive I've used (behind Samsung which I'll never touch again) but considering I've used approx 100 WD drives over the years I'd say thats a pretty good percentage.
The best drives in my experience have been Seagate ... I've used more of theirs then WD's & literally the first one I've had a problem with was today when a week-old 320gb 7200.10 SATA drive started making intermittant sounds like a marble bouncing around inside a soda can! :Q
Bottom line however is that every HD has a 100% failure-rate so backups are key.