Rather than risking my data with the replacement Samsung hard drives I decided to sell them for a huge loss on eBay (under half price). Guess what? One of the guys is reporting that the SP1614N (160GB) hard drive I sold him is in fact an SP1213N (120GB) - Samsung have stuck the wrong label on the drive. Not only this but it already has errors on it! If this isn't a lesson to be learned then I don't know what is. Stay away from Samsung!

*Update*
Someone emailed me saying

"Those drives stacked right on top of one another are probably failing due to heat. I like to leave at least an inch of air space on top of and below each drive."

Just because they are stacked in a photo doesnt mean thats how they were operating. As the posts say... they were in different computers (a total of three) and did have gaps between them. In two of the computers they had fans blowing directly on them. Also, as this post indicates, one of the eBay hard drives was DOA according to the recipient. When I sent it, it was packed in a hard drive box, in a bubble wrap bag, surrounded by foam chippings in a big cardboard box... so I don’t think it was damaged in transit.