It was in back 2007 when some folks from Google presented a very interesting paper on the 5th USENIX Conference on File and Storage Technologies (FAST’07). They looked into more the 100,000 disks over a period of about nine months. From its main findings the following points are particularly interesting:

• Only 44% of the failed drives showed relevant information in the SMART data
• Disk activity has no big impact
• Neither does temperature

I was quite astonished! If you are interested, please go ahead and read the full paper here.

Also, this posting might be of interest to you, including the discussion following it. It also discusses another study which found that the disk type (SCSI, SATA, FC) is pretty irrelevant.