Back on topic, I have an older Seagate Momentus 500gb 5400rpm drive that I got from Amazon a few months ago, and its been working perfectly. In the past I've had bad experiences with Western Digital drives (had several fail in servers at work), but rarely have I had issues with Seagate drives. And the drive I got was 5400rpm so it should run a bit cooler than the 7200rpm drives.
Having said that, ALL hard drives which are mechanical (not SSD) are definitely prone to failure. Check our reviews on Amazon for all the brands, and you'll find a mixture of very happy customers, and very unhappy ones from failed drives. I just checked the WD Scorpio Blue 500gb reviews and they're mixed just like they are for the Seagate drives.
Oh and also I have about 10 Seagate external hard drives ranging from 80gb to 640gb, different styles, and not one has ever failed on me. Some are portable drives, some are desktop drives, and they've all been great.
Looking forward to the day that internal and external SSDs become reasonably priced (for 500gb+ capacity), they're just a bit pricey right now, and current consoles just don't take advantage of the speed gains for Sata III/SSD.