There seems to be a bug in the Atheros wlan driver in Ubuntu-9.10. The driver frequently disassociates from the access point, disrupting the network connection. See also bug report https://bugs.launchpad.net/linux/+bug/414560
A typical dmesg excerpt:
[ 1881.988111] wlan0: no probe response from AP 00:15:e9:13:47:60 - disassociating
I have seen this on an Asus notebook. The only solution seems to have the Atheros modules load again.
To make this a little bearable, I created a small Python program to test and fix the connection to the access point by unloading and reloading the Atheros modules on the press of a button.
download: atheros_reassociate.py
. . . . . Ir.S.S.R. Kwee Computer Consultancy