I've noticed since the first set of 500GB + Hard Drives hit the market that more and more of them have been failing fairly quickly, we order HDD's almost on a daily basis. I have had seagate, western digital, hitachi and others all have a high failure rate from 500GB to 2TB. It doesn't seem to be isolated to just one manufacturer. I have tried several different wholesellers / retailers, so it isn't coming from just one place (sometimes a single supplier will get a large batch of bad drives).
Interesting. If what you say is true, does it mean that the higher density platters are less reliable? Though you can't rule out the possibility that you were just unlucky... This is what WD says about their Caviar drives: "Kindly take note as all drives are designed around a 5 year life span. Our drives have less then a 1% annualized failure rate..."
I'm unconvinced, honestly. There have been problematic drives (Seagate 7200.11 springs to mind), but on the whole, large drives don't have any higher of a failure rate from what I've seen (and someone I know at Seagate has told me that their 7200.12 drive has a very low failure rate based on both internal testing and the number of returned units).
It could just be bad luck. How many drives do you have?