There as a limited range of early WD drives that had firmware incompatible with the Mac and caused kernel panics due to their motion sensor. However, that seems to be limited in scope. I myself have used WD 250 and WD 350 GB drives without kernel panic problems in my MacBook. This is on a machine that gets moved throughout the day.
BTW the have a 500 GB unit in volume release now. (Just days after I installed a Samsung 500 MB drive in the MacBook)