Recently installed ubuntu 12.04 on a fresh and clean system. While it works like a charm, a very irritating issue was that the inbuilt wireless card was not working. The ethernet connection using wire worked fine. Googled a lot and wasnt able to figure things out. Finally, backports saved my day. Here is the procedure I followed incase someone finds it useful.
sudo apt-get install linux-backports-modules-cw-3.8-precise-generic
Some generic headers and libraries:
sudo apt-get install linux-headers-generic build-essential
Download this file and extract it at a location of your choice.
Navigate to the extracted directory using terminal and try:
make defconfig-ath9k make sudo make install
Reboot the system and ideally wireless should work!
Hope it helps.