I noticed was my wifi (Atheros AR5001/5007EG) stopped working after I upgraded to Karmic Koala. I searched endlessly on Google without any answer. Then, I remembered that Karmic comes with newer kernel 2.6.31. And ath5k kernel module hasn’t been loaded yet into this newer kernel.

So, I simply executed

modprobe ath5k

in the terminal.
And in an instant, I saw my wifi connected to my access point.
The command loaded the module into the kernel.

Hope, this helps.

Cheers!