I recently upgraded from Ubuntu 9.04 to 9.10 only to find my wireless was no longer working. Using the previous backport solution I had mediocre wifi signal performance in 9.04, but it was reliable. I read that the ath5k drivers are now much improved and preferred over madwifi. The following solution gives excellent signal performance and reliability for me:
1.Comment out (prepend with a "#") all "blacklist ath5k" statements in files in /etc/modprobe.d/. The prime suspects are the following two files:
/etc/modprobe.d/blacklist-ath_pci.conf (it will be in this file by default)
/etc/modprobe.d/blacklist.conf (you may have put it here in the past)
My particular problem was that I had a copy of an old blacklist.conf file in this directory named blacklist.conf.old with "blacklist ath5k" in it, and although modprobe says it will disregard files not ending in ".conf" in the future, it still currently applies the commands within and keeps the module from loading.
2.After removing all files with this command you can test your wireless with "sudo modprobe ath5k." It should fire right up if all is well.
This is an updated version of a previous post covering Ubuntu 8.10.