Not that I’m going to do this, but …
Would I likely see much difference in performance between using rolls of Tyvek housewrap on a home vs. grabbing stacks of those free FedEx and USPS Tyvek envelopes and stapling them to my house sheathing?
I wouldn’t think it would be as effective. Perhaps if you overlapped them and sealed them with tape, it might work. Isn’t the point of Tyvek to be a moisture barrier?
My snowboarding gloves are lined with Kevlar… but that doesn’t mean I should use a bunch of them to make a bulletproof vest. =P
The glues in the tape you would use to connect the small Tyvek sheets would be the weak point and would degrade much more quickly than the Tyvek material it’s securing so it’s effectivness as moisture barrier after a few seasons would be poor. Beyond that the the labor vs cost benefit involved in doing this is absurd unless you’re wrapping a dog house.
I also agree that the Fedex envelopes would be ineffective housewrap, since they’re not continguous. Also, Tyvek housewrap is probably cheap and quick enough to install that it wouldn’t pay. However here is an article from Wired Magazine about a guy who furnished his apartment using Fedex packaging.
There’s also the minor point that what you are proposing is not exactly kosher - stealing a mess of envelopes to grace your house.
Well, they do give them away for free… 
I’d be more concerned that a FedEx Custom Critical driver would show up and attempt to load the house onto the truck when they see this big thin covered in FedEx logos.
And yes, I’d expect FedEx to get really unhappy with you for misuse of their materials. How many drop boxes would you have to go to to get enough to wrap a house, anyway? I think the guy at the Kinko’s would be really curious why you wanted 10,000 envelopes and don’t even have a FedEx account.
When you order bulk shipping supplies from the USPS they have a thing on their site, before you are allowed to order, that specifically states they can only be used for sending and receiving US Mail. Since tampering with mail is a pretty serious offense, I don’t think I’d want to risk “stealing” from the post office. Stick with FedEx; they may only sic lawyers on you.
Those envelopes are not that big anyway. By the time you got them all taped together securely, there’d likely be more tape than envelope… if your neighbour’s didn’t kill you before you were even finished.
His neighbor’s what? 
Besides, the postage on the house if you moved would probably be insane.
Well aren’t you hi-larious. Excuse me for making a typo, sir, and not wasting a whole post just to correct it.
But you did waste a whole post to complain about it.
I still don’t get what it was supposed to say.
Should have been “neighbo(u)rs” - the poster was abusing apostrophes. As I’ve read previously, "an apostrophe does not mean ‘here comes an S!’ "
One stupid nit pick deserves another, as they say. Or don’t. I don’t feel the need to correct a typo in what’s otherwise a correctly written post. I don’t get why people do this. (Plus it really wasn’t funny.)
I was posting while I was tired and accidentally put an apostrophe where one does not belong, as occasionally happens when a person types very quickly. Someone felt the need to make a stupid joke about it. I guess I’m supposed to be embarrased? Me am know English my very well, thank you.
Point of fact: I laughed.