Unibody MacBook: Microphone
The tiny holes for the microphone couldn't be closer to the fan exhaust except by putting it actutally behind the machine. I'm guessing it will be for "casual recording" just like the poor speaker on iPhone and iPod touch 2G are for "casual listening".
The Ambiant Light Sensor is next to the iSight on the whole notebook range now, which makes a lot more sense than before:
there used to be two sensors, one behind each speaker grill, and the computer was using the average of the two. Except it was picking up the light from the display, so it could go in a loop... Good that it won't happen again.