The first thing to remember is that indoor air quality is NOT an insulation or vapor barrier issue. It needs to be managed as it's own issue.
The second thing to remember. There is a significant difference betwwen poly & kraft faced insulation, and that difference is not vapor barrier, but air movement barrier. This is an important difference, especially where the wall / ceiling material is not an air movement barrier (Wood t&g panelling is not an air movement barrer. Every joint & seal will allow air to pass though). If you are using T&G wood on the ceiling, you must install poly or another air movement barrier. I've been involved in trying to repart the catastophic problems created by not doing this, and it can be very expensive, both in lost energy, as well as structural damage (One such project I've been involved with, a house less then 15yrs old, now needs about $100,000 or repairs, repairs that would not have been neede if the put poly on the sealing under their T&G.)
the third thing to remember. If anyone tells you that the "house needs to breath" in this manner, ignor them!