Above a surtan point heat will start lowering the life expectansy of a harddrive. If the airflow is bad around the cards (witch it is in most cases) and you have a drive that's running hot I do belive there's a chance of damaging components on the controller ther drive sits on aswell as cards close by. You're much better of monting the drive somewhere else in the chassi.
In the new tower (Cooler Master Stacker) for my A4000, fans will keep the drives cool (coolermaster got this nice module to mount four 3.5" drives in three 5.25" slots with a fan in front of it and rubber barings on the sides for lowering noice).
I've killed a drive by keeping it in one of those plastic harddrive racks without a fan you can get for like 10$, that's why my new rack is made out of aluminium and have a fan (with controller on front) aswell as a heatprobe, display and alarm system (nice little thing that set me back over 50$). Just to be on the safe side and to lower noice even further in this tower I got myself a CoolerMaster Aerogate3 to controll the 4 fans that sit in the tower... it also have 4 heatprobes (and display) so I'm thinking of having it check the PPC, 060, Voodoo3 and my 9Gb UWSCSI drive.
Yes I'm letting go of the firm grip of my wallet to finaly give my A4000 a pallase of a tower. :-D
