My HD is a regular 7200rpm drive, mounted in a 5.1/4 bay with rubber mounts (to kill noise) and it easily reaches 55c under normal use. With case temp of 25c.. That's uncomfortable high temperature, but as long as it survives a couple of months more, I'm happy. Then I'll move to a new house, and have my hd's watercooled. (big system rebuild..)
So cooling the HD can certainly be neccesary. When I'll watercool the drives, I'll use som copper sheet and 22mm copper tubing. Make two 90degree "angle iron" of the copper sheet so the side and top of the drive will be in contact with the copper. And have the drives "on their back" so heat from the pcb radiates up in stead of being "stuck" under the drive..
