If you ever consider buying external hard drive, do not ever look at WD My Book. I bought about a couple of month ago WD My Book PE 500GB and was happy.. at the beginning. Once I have started using it and freeing my puter's drive by moving content to WD I found out that it has problems. And very very annoying ones.
This external drive can disconnect itself anytime it feels like. Actually its not disconnecting, but just appears like parked or something - you still see the drive in My Computer , but you cannot copy anything from it. You have to physically restart it by pressing the button on its side. This happened to me always, except maybe cases where I just needed some small file and was quick enough to copy it before drive shuts itself. So never buy this drive. Never.