This review is from: Western Digital 1TB SATA 6GBps Power Saving Internal Hard Drive - Caviar Green (Personal Computers)
Replacement Green drive (recertified, WD don't replace with new) has now failed after 4/5 months. Very similar problem to the 1st drive, would disappear for a time then reappear temporally.
managed to copy my stuff off drive over some days. I think its a temperature thing.Fine when its cool then when it reaches normal temperature, it has a rest.
I have other WD drives 3 velociraptors and a black 1tb and they run fine.
WD do have a good advance RMA system. so if it does go wrong you will get it replaced quickly. Always backup your stuff! if It can fail, it will fail, its just a matter of time!