Comment 20 for bug 721449

So... I finally resolved the issue effectively without any remaining restrictions. But in order to do that I made a rather 'radical' move...

I installed the carl9170 firmware and compiled the carl9170 kernel module from compat-wireless package. (This might take about 10-15 minutes of your time)

Firmware:
http://wireless.kernel.org/en/users/Drivers/carl9170#Firmware-1
Kernel Modules:
http://wireless.kernel.org/en/users/Download/stable/#compat-wireless_2.6.38_stable_releases

!!! Warning !!! I won't guarantee that this won't harm your system. I will NOT be responsible for any damage.

1) To install the firmware, I ran:
sudo wget http://www.kernel.org/pub/linux/kernel/people/chr/carl9170/fw/1.9.2/carl9170-1.fw

2) To compile and install the module, I downloaded and unpacked:
http://www.orbit-lab.org/kernel/compat-wireless-2.6-stable/v2.6.38/compat-wireless-2.6.38.2-2.tar.bz2

If it is not already the case you must boot to the kernel 2.6.38 (I had to do this because I was using kernel 2.6.35 until now)
Open a terminal and change dir to the one you just unpacked and run:
 ./scripts/driver-select atheros
make
sudo make install

Either you make a reboot at that point or you run following commands:
sudo make unload
sudo modprobe 'carl9170'
(also have a look into 'ReadMe', it says essentially the same)

Unplugging and plugging my usb device in again, I could already enjoy a stable and fast wifi connection.
(If at some point you want to uninstall these kernel-modules again just run "make uninstall" in the directory in which you ran "make" from...)