First, please don't post to this thread unless you have the issue described by the original poster.
Second, I discovered the problem Friday afternoon (received via FEDEX at 2:40pm) and knew instantly what it was (engineering background) and confirmed it by reading the testimonials on this thread. So on Saturday morning, I went to Apple in Mission Viejo, California and explained the problem was a bad capacitor that only failed under heavy use, such as when WPA2 was enabled on a slow (or sustained) link. Someone claming to be named Smith took my phone and receipt in the back room where the geniuses scuffed the delicate (mirrored) Apple logo and plastic backing before sending Smith back out demanding I substantiate my claim of a defect. I had already brought up this forum thread on a Mac and pointed it to him, as well as giving him directions to simply go back and google for "iPhone 5 WiFi Problems" to find it again --at that point, this thread was 7 pages long (and not picked up by all the blog sites). Smith came back from the back and reported that they were denying my exchange on the grounds that they could not reproduce the problem.
[To try and reproduce for Apple Store, I had started downloding a pile of apps while doing a speedtest, but the problem would not exhibit because their network was too fast and did not have WPA2 encryption, meaning the RF in the phone did not ever "heat up" enough to trigger the failure. Someone walked by and confirmed they had a replacement in-stock, but it had 16GB more than mine and apparently Smith didn't even want to offer me the option to PAY the difference (though I should not have had to). Smith handed me back my scuffed up phone, took my email and phone number and said Sorry, they could not confirm any problem and would not exchange the device.]
After being denied a replacement in Mission Viejo, I went directly to Apple in Irvine Spectrum where the front-person greeting people told me they were sold out. I indicated I was there for an exchange not a sale and he went running back in the crowd. A young girl in a "robotic state" emerged with an iPad to inform me that they had no replacements and I asked to speak with the manager. A manager named "Matt" came out and informed me they were sold out and that he didn't want to take my unit and send it overnight to Cupertino for analysis, despite my claiming to have a confirmed bad production unit with decades of professional experience and background in engineering to back up my claim which was being repeated by others online. (I did hang around though and re-downloaded all my apps that I had secure-erased from the phone a few times using their super-fast 37Mbps WPA-less hotspot, since only a moron would run a WiFi hotspot at home without WPA2 enabled.) I can't really blame this store because they simply didn't have any stock (even a model with an additional 16GB). The only real issue I had here was that they were at or slightly over occupancy limit. A few moments later, this thread became unavailable due to "maintenance" on the Apple site.
Also stopped by the new huge Verizon Wireless in Rancho Santa Margarita, CA but their hipsters had not even seen the new iPhone 5 yet.
So I still have an iPhone 5 that I did not need this thread to tell me has a hardware issue --I burned through my Saturday visiting two Apple Stores and Verizon Wireless store (despite getting up and ordering my unit online during the first hour a week earlier) and have scuffs on the phone (also leaks light from a crevas between faceplate and silver bar one inch from the upper left corner). It's going to be returned to Verizon Wireless, the only quesiton is whether their online customer service will be sending me an advance replacement in order to keep me from giong back to my AT&T account.
