I've been dealing with a lot of the "disk not ejected properly" error messages on my iMac (mid-2011). I've got it connected through Firewire. I've tried using both ports, the USB port, wiping the drive and starting over, I've checked for firmware updates and I've disabled the drive's sleep timer through WD's software. I'm at a complete loss as to what is going on. I'm hoping to find some assistance here. =)
I also wanted to note that I've also have had trouble getting it to re-mount randomly after it randomly ejects.