I had bad luck with Western Digital in the past and swore "never again".
I received my Mac Pro last Friday and bought an additional WD 500gb drive, basically as it seems to be as quiet as they come. Certainly is the case so far, have it filled with 350gb of music, photos and video, it is definitely a tad quieter than the Barracuda (500gb) that came with the MP.
If it doesn't work for me, I suppose I have no one to blame but myself, but system is "go" at the present.
Oh yeah- it is a BLAST to install a drive with the MP. Even more fun than the G5 PM.
~gtd