Well proper computers have various intake and exhaust slots in the main body, so a laptop cooler will actually be blowing air into the system. However, Apple like to wrap their toys in enclosed aluminium shells so you may have problems with standard laptop coolers.
If a processor can not run at 100% for 3 years (retail) or 1 year (OEM) while keeping at safe temperatures then it is faulty. You don't buy hardware expecting it to only handle light loads Heat will kill it though, so keep that in check.
if your really paranoid you could always down clock it, reducing heat though obviously it will take a lot longer to render. But I wouldn't bother. Just make sure your pc is resting on a hard surface rather then a soft one and i'm pretty sure that resting it on a heat conductive surface would help as well