Some day I really should change my signature on here to say something like, My comments reflect what I've learned over the years working on houses, tractors and what ever else I'm commenting on. I'm not educated, not the most knowledgeable, but believe in what I say and will always try to give the best advice that I'm aware of based on best practices and overall results.
Another poster likes to go into extreme details about insulation. I'm sure that he is very smart and knowledgeable in what he says, but none of it really applies to common building practices and how to get the most measurable results from proven methods and products.
I'm not against house wrap, but by it's very design, it's meant to allow air to go through it. So yes, it will always leak air. My comments also apply to what is commonly done in home building from what I've seen. I try to never go to absolutes because if you have enough money and don't care about spending it, there is always a better way. Kind of like being into riding mountain bikes on weekends twice a month and spending $600 on a seat that's two ounces lighter then the one that came with your bicycle, like a friend of mine did. It made him feel better about his bike, but he will never notice the difference while out riding his bike.
The other thing is that there are a lot of products that are pretty much impossible to install properly, or that workers will take the time to go through every step when building a house. House wrap is one of those products that could be a lot better if more time and effort where put into the install, but it's just not done very often. The huge advantage of Zip Siding over common OSB and house wrap is that it's pretty hard to do it wrong. If you don't put the tape on it, everyone will know it's done wrong. If you fail to tape a seam on house wrap, nobody really cares.