Some hard drives are more reliable than others.
I've had good experiences with most drives, but some stand out as poor. The Seagate 160gd, the Western Digital 200gb. And most recently, the Seagate 3tb.
I'v just read an article that confirms that last drive as poor.
After buying just a few of them, they went onto my Blacklist, and it's nice to see that I was right.