There have been some posts here about adapters using RealTek's 8188CUs chips being recognized but not working. You enter the pass phrase, it thinks about it for a minute or so and asks for the pass phrase again and repeats. I've used and recommended downloading and installing RealTek's driver and blacklisting the 'built-in' driver if necessary. That solution worked for me.

The good news is that on 12.04, Xubuntu 12.04 and Ubuntu 12.10, after updating my Edimax EW7811Un appears to be working with the built-in driver with no issues and no file edits. This adapter - and presumably its clones - is IMO a great solution for older portables with B or G speed wireless or portables with problematic wifi chipsets. It only protrudes from the USB port about 1 cm. My only niggle is that the blue activity light stays on continuously rather than flashing when active. I believe someone had a file edit that would fix the light-on-continuously problem, or there's always black tape .