Wifi Problems [Macbook air 2012 Mountain Lion]

Question

I have a new (barely 2 weeks old) Macbook Air fresh from Shanghai.  It is running the most current OSX 10.8.2 with the newest update.  All apps are up to date.  It has 8gb ram and a core i7 processor. 
The wifi is extremely slow (I am seeing rates from a couple kb to maybe 100kb/s).  The wifi icon in the upper bar displays full strength for my home wifi (WPA2 secured running N-band).  However, if I go more than a 10 feet from the router the signal appears to drop off dramatically (speeds become lethargic, nearly 0kb/s) although the icon still displays full strenth.  The only way I can get half-decent speeds is by physically sitting in my closet with the router.  Clearly, this is not ideal and hopefully is not the norm for a brand new system like this that is meant to be an ultraportable. 
Another symptom I have noted is that when the macbook is connected to the network, the speed of all other wifi-connected devices also drops off - though not as dramatically.  
The wifi connection problem appears to be not just with my home network as it is also unbearable with any wifi network I've tried EXCEPT the apple store (so of course the apple genius wasn't convinced).  
I have tried many things to fix this including:
bluetooth is turned off
no other devices are connected
reset router
reset wifi setting on computer and turn on/off
reseting NVRAM
changing network (I have tried 2 home networks, starbucks, a portable hotspot, and my school's wifi)
So far, as I mentioned before, the only way to get above 20 kb/s is to sit inside my closet.  This network works perfectly with 3+ other computers and any cell phones/printers/etc that have been hooked up to it, many of which are many rooms/walls away.  Also, even sitting next to the router, speeds are still 10x slower than other devices.
Any help would be greatly appreciated!
Thank you!

Answer 1

     O
I had the excact same issue, I have now restored to OSX 10.8.1 rather than update to 10.8.2? downside is I cannot use iPhoto because it requires 10.8.2 to install
Strange thing is when i updated to 10.8.2 and logged in as a guest user i had no internet problems, but as soon as I switched back to my account login the wifi issues came back?
I even spent 2 hours on the phone to my internet service provider thinking it was my router giving up.
It was only through luck that i picked up on the fact that it didnt cause issues before i updated, but only after the update did the issue raise its head.
Im a loyal apple user,  I also sell apple products through a reseller bar inside the store I work, but im starting to loose faith.
Lets hope this is a bigger issue than just a handful of users, that way apple may get a fix out for this
( Fingers crossed)
iMac late 2009 24" iPhone 4s 16GBIpad 16GB 3rd GenApple Tv 3rd GenMacbook Air 11" mid 2012
Wayne