Mac mini Audio Input

You are basically right, yes. The Intel mini has an audio input which is 'line level', making it compatible with signal voltages from such things as stereo systems. As such, standard microphones with lower output voltages will not work without a pre-amp (or an external USB device such as the Griffin iMic). However, microphones which have pre-amps built in (many electret-condeser types for example) should work just fine, as would most USB microphones.

Thankyou for your post, it covers the same issues I am wrestling with now as I try to switch from PC to Mac. The lack of a simple microphone input on my mac mini sullies what is actually a great machine. I wonder if this was an oversight by Apple?

There's no indication that it was an oversight - indeed, it would be rather odd in an otherwise thoroughly considered and well designed product for Apple to have missed something that obvious. I would be inclined to think it was an intentional choice to use line-level input, allowing users who need microphone input the option of using typically better quality amplified devices, or USB audio input. Other Macs have also used line-level audio input, so the mini is not alone in this.

It's easy to overcome with the right mic or something like the Griffin iMic ( http://www.griffintechnology.com/products/imic/) or any of a plethora of USB mics.

Thanks Andy, yes you are right, I was just to used to PC style, I can see the advantages of USB and bluetooth based mic and headset now, much better...............