start/stop puts the most stress on the fans and starting / stoping them too often will wear them out faster than just running I would suggest not stoping them and just running them slower as this should increase their lifespan
i have one of those Sflex 1200 rpm case fans and it's still going after around 7-8 years running almost 24/7 although it's been kept faily dust free most of it's life.
Note: the reason for this is when the fan starts up the bearings have the least amount of lubrication and this puts more wear on them than just running.
Intel Xeon X5650 @ 3.53Ghz 1.2V : Prolimatech Megahalems w/ Sythe Kama Flow 2
EVGA X58 SLI LE : 24GB of Samsung DDR3 1600 6x4GB 1.35V : EVGA Geforce 480 GTX
HDDs 512GB MX100 SSD, 2TB WD Black, & 2x 2TB HGST
Viewsonic VA2626wm & Gateway KX2703 : Asus DRW-2014L1T : OS Winows 7 Pro Sp1
Onkyo TX-SR501 HT reciver + 5.1 speaker setup : Antec P280 : 750 watt EVGA G2
Last edited by Arcanedeath; 11-26-2012 at 10:53 PM.