Interesting paper on the current differences between enterprise and consumer grade drives.
http://www.usenix.org/events/fast03/tech/anderson.html

Esp. see section 3.5 on reliability.
- Consumer drives are designed for 2400 POH (power-on hours) a year - running them for 9600 POH will double the failure rate.
- All drives are designed to run as cold as possible (25C room temperature) - an ambient temp of 40C will double the failure rate.