Ahhhhrrrrrwheeeewwwww…. Ahhhhrrrrrrggghrrrrwwhewww… those are the snoring sounds from many people when faced with this subject. To me, however, I take vapor barriers in residential construction very seriously (and vapor retarders). You should, too, if you are planning on having a new home designed and built soon, if you want it to be a healthy place for your family, and energy efficient.
The way things used to be done and they way they may be done now is probably wrong, in many homes. Why? Because it can be a confusing subject, with as many opinions as there are people involved in construction. Most people in the construction industry do what they are used to doing, what they have reliable cost information on, with dependable subcontractors who perform reliably for a set price, so that the builders can make a living for a reasonable cost!!!!!
Even so, there are tried and true solutions that can be used, products and materials that have been around for decades that work just fine and deliver a true value: good quality for reasonable cost. For instance, most homes these days are wrapped in a big white sheet of material. It really is not doing what you may have been led to believe, or may be doing it too well, which might cause other problems.