Hi!, im trying to update the 8u2 to solve the problem with Linux. I did what this tutorial say: (http://arduino.cc/en/Hacking/DFUProgramming8U2), but when I select "USB" from the "Comunication" menu, the next message appear: "AtLibUsbDfu.dll not found" "Could not load dynamic library". I found that library in the bin directory of FLIP. I'm using Windows 7 x64, but I try too in a PC with XP x32 and the same. Any idea?
PD: Sorry for my english 
Google "AtLibUsbDfu.dll not found"
MarkT:
Google "AtLibUsbDfu.dll not found"
Google?, what's that?! 
Look for a lot in google but nothing works. I did not find too many people use Arduino and have this problem. Some say I have to reinstall the programmer driver, but I'm using arduino to update. Someone who has had the same problem can help me?
I was having the same problem and solved it. Not before I stumbled across many posts left incomplete like this one.
To solve it I followed the connections on the first image here (Proyectos Arduino - Ikkaro)
Then went into the device manager were it said that there was a problem with the driver.
I proceeded to install a driver from the: (C:\Program Files (x86)\Atmel\Flip 3.4.1) folder
The driver appeared ok in the device manager now.
I proceeded to select a device and open USB, to which i got an error message : USB cannot comunicate
In my case, I discovered the reason was I was not choosing the correct MEGA (I had the at90usb82, but I'm using the AT16u2)
best of luck!
Para el Arduino Uno que compre este año 2014, me funcionó con los siguientes cambios:
DEBE usar la resistencia de 200 ohms
Aparece es un puerto atmega16u2
Usar los Drivers de Arduino y no de Atmel:
C:\Program Files (x86)\Arduino\drivers
Ya existe Flip ver 3.4.7
Usar el Hex que viene en la carpeta de Arduino:
C:\Program Files (x86)\Arduino\hardware\arduino\firmwares\atmegaxxu2
Arduino-usbserial-atmega16u2-Uno-Rev3.hex
Muchas gracias por el tutorial, el único que me funcionó.