I Bought 2 of these drives last year. I have one drive mirroring the other, and so far both drives have performed well (about 9 months to date). They are very quiet, and I have been impressed by the speed of the drives too. These were replacements for X2 Seagate Barracuda drives I had bought first. Both drives slotted straight into bays in my MacPro, installing new system and software (Mac OS 10.6.8 snow leopard) was a 'piece of cake'.
A word of warning if your considering the barracuda drives, they were so loud I had to return them!
Overall the WDs appear to be stable, I am using them for pretty intensive work, and so far so good. Would I recommend them - Yes.