I was doing some research and thought these three links might come in handy if you're interested in case/HS fans, noise and longevity.
http://www.hardwaresecrets.com/article/Anatomy-of-Computer-Fans/1039
http://www.frostytech.com/articleview.cfm?articleid=193&page=1
http://www.silentpcreview.com/Anatomy_of_the_Silent_Fan
http://www.hardwaresecrets.com/article/Anatomy-of-Computer-Fans/1039
http://www.frostytech.com/articleview.cfm?articleid=193&page=1
http://www.silentpcreview.com/Anatomy_of_the_Silent_Fan