This appears to be a kernel bug. Connections seem to hang. I am not sure which levels of Ubuntu this affects, but it happens to me in 12.10. It is impossible to update the system, because it never finishes downloading the package lists.
I am going to try 12.04 next. I had been using 12.04 on an older system with the same WIFI board, but I got a new system, and thought I would put in 12.10.
[ 73.084718] ath5k: ath5k_hw_get_isr: ISR: 0x00000400 IMR: 0x00000000
[ 802.024954] ath5k: ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
[ 1281.874667] ath5k: ath5k_hw_get_isr: ISR: 0x00000080 IMR: 0x00000000
The Windows driver for this board works just fine, so hopefully 12.04 will work too.
I found this bug report, but I do not lose my wifi connection:
After installing Ubuntu 12.04, I get no driver messages in the kernel, but internet is very slow with ubuntu, even when bringing up my DSL modem's built-in web page.