Heat can and does trash drives. Heat and static electricity are the enemies of all electronics. HDDs with more cyliders spinning faster do produce more heat. Manufacturers have switched from aluminum to glass cylinders to combat these effects.
Case temp isn't CPU temp or HDD temp -- don't fall into that trap. Air and thermal flow varies tremendously from case to case (with different HDD and CD drives and cables, fans, etc.). Redjake, consider yourself lucky. If your hard drives haven't crashed, I doubt it's "proof". It's luck.
growingnut007 has both many and newer drives, which all point to heat issues. This is a far as I can go with the "diagnosis" given the lack of details, but one would naturally look for common threats due to the fact that several similar drives suffered the same fate.
All parts in modern PCs have maximun temp ratings, usually around 50-60 degrees C. The MTBF hour (failure) time goes down remarkably when temps, ambient or on the part itself, rise above these recommended temps. If your drives or other componenets are either near or at the point where they are too hot to touch, they need help cooling right away.
Manufacturers have noise and heat on their minds when it comes to faster, bigger drives. Some ambient noise "solutions" included insulation that does indeed cut down on noise. but traps heat as well. Western Digital warns people about stacking firewire and usb drives because of heat considerations.
I think that we will see more kinds of solid-state storage solutions in the future -- less heat and moving parts make a more stable storage device.
Edit: heya1256 talks about the old IBM "deathstars". My 2 always ran hot, even with fans, and neither lasted more than 8 months. I have old 6 gig drives running virtually every day since 1998 that are old and slow but cool to the touch.
Here's a link from Hitachi that promotes a new heat-related feature