Riick:
JFYI, when DuPont originally attempted to secure approval for Tyvek they couldn't pass the water-hold-out "boat test", so they got it approved as an "air-barrier", even though the code doesn't require an air-barrier. They then proceeded to advertise it as a product which did everything and, unbelievably, many AHJ's accepted it as the code mandated weatherproof barrier (the code specifically called out asphalt saturated rag felt or approved kraft paper, in the lathing section it calls out two layers of Grade D paper behind stucco, but the AHJ can accept an approved alternative, an alternative which DuPont didn't achieve). DuPont eventually got a new test approved, called the hydrostatic pressure test which Tyvek (and other plastic wraps) could pass, so they are now an approved alternative to the code mandated products.
In our area, not even the cheapest of tract builders use plastic wraps because the potential for leakage is so great, I sometimes see it in architect specified commercial projects, and I see it all the time on ignorant DIY projects. Another problem with them is that surfactants eat right through them, the tannins in redwood and cedar, as well as the limes in stucco and fibercement products. I know of one McMansion builder who uses both Tyvek and asphalt saturated felt to obtain both an air barrier and a waterproof barrier, while this may be a good idea I've called Tyvek and they say they have never tested the products for compatibility. That being said, I like Tyvek's Flexwrap for flashing round windows and use it in conjunction with asphalt and kraft based products, I also use it to wrap around plumbing penetrations in shower walls, since the stupid shower valve manufacturers don't build flanges into their valves for sealing. In homes I've built 30 to 40 years ago my biggest failing has been dry rot behind shower walls from water penetrating my waterproof barriers at the plumbing penetrations.