[houltmac]

Yuiichi is completely right, the thermal envelope of the Mac mini is much better than the MacBook so the fans won't be as noticeable as often. That's the price we pay for demanding thinner an thinner notebooks I guess. Take his advice regards how and when the fan comes on though, it would be interesting if his assumptions are wrong.

In terms of components being damaged, no, a fan won't do any harm. Basically it's doing as it's intended to do and that's a good thing. When you can't hear the fans anymore you need to worry. Something like iStat would be good in that case. If the fans don't behave as they should (and are by the sound of it) then the CPU, GPU and so on can overheat, likely causing a kernel panic or shutdown and possibly damage to the components.

Right now I'd say you are good, the only thing it can hurt is the life of the fan, but fans are cheap and sturdy.