My Atheros AR5004G (AR5213 chipset) wouldn't scan for networks successfully:
iwlist ath0 scan:
ath0 No scan results
I searched the archives for this problem, it was mentioned quite often - sometimes with the AR5004G as well. I asked about my problem on the IRC channel, svens suggested me to try a patch he wrote (he used an AR5213 chipset as well) to disable rfkill in the module. So I tried this patch, and disabled rfkill, and now it works just fine. Since rfkill doesn't have to be disabled (it only is when you load the module with modprobe ath_pci rfkill=0) it might be a good idea to patch the module by default, it saves users a headache trying to find a fix.
Svens' patch:
http://svens.ath.cx/rfkill.diff
Sam