not to go way off topic.....but......
"Yea, over a long period of time meaing 10-15 years ;o."
A well-cooled AMD system, without overclock, is rated to last about 6 years. Overclocking decreases this average lifespan relatively.
"Also, if your CPU fan dies, your processor will switch off to save itself, as long as it's relatively new."
This feature is BIOS-dependent, it's not always automatic, either. In many cases, you have to go into the CMOS and set the warning/shutdown temp of the CPU manually. Even then, you need to be vigilant in the selection of the shutdown temp. I set mine at 60C. Since it doesn't hit 40C under a full load, if it ever reached 60C, something requires immediate attention.
"Also, you do know that 10K rpms builds up a lot of heat, right? Heat = lowered life of components"
Certain types of drives are prone to more heat. From SCSI to PATA to SATA, the heat difference can be very distinctive. SATA drives are notorious for running hotter than their now passe counterpart. A lot of heat? Not really. Only warm to the touch. Heat is never a problem when you're equipped with proper cooling.
"I believe powering down when sleeping and powering on when awake is the best idea."
This is, more or less, preference. The only system that should be running all the time is a server box of sorts. A workstation should be powered down at least once a week. I always shut it down when I leave for work, if I have nothing in the "queue", so to speak. Whether it's virus scanning, defragmentating, downloading, backing up, or whatever else I can put this rig through.
"I also really doubt that it spins up to max speed the second you push it on, if it did, it would probably rip the disks right out of place in the hard drive."
Here comes the clue train, last stop is you. Everything accelerates. If you were to break into a run from a walk, do you achieve maximum velocity instantaneously?