Returning to our thread on pin 2 versus pin 3 hot from the week of 1/3 - 1/7, we've had a few inSync readers inquire about mic inputs on mixers.
Technically the same principles apply. If the mic and mixer (or mic preamp) are different polarity from each other then a polarity reversed cable can be used to straighten it out. Two additional points:
1) Microphones and mic inputs arguably seem to much more closely adhere to the pin 2 hot standard than line level gear so your chances of running into a mismatch are lower to start with.
2) Many mixers and preamps have a polarity reverse switch (sometimes mistakenly referred to as a phase invert) right at their input, which will accomplish the same thing as a custom cable.
You may also decide that in some instances it doesn't matter. For example, it may not be all that important to have the guitar player's cabinet miked at the same polarity as the singer's scratch vocal track. This reopens the old absolute phase question again, but even those critically concerned with that can often find situations where they'll agree it isn't as important.