First of all, thanks for your time putting together your wpasupplicant howto.  It helped me greatly, although I was mostly interested in getting the roaming feature to work, which you don't mention.  I thought I'd send in how I was able to do this on my Fujitsu Lifebook with built-in Atheros card.  I'm using Debian 'testing', currently 2.6.17-2, wpasupplicant version 0.5.5-2, and madwifi-source 0.9.2.  I'm also using ifplugd.

I normally just carry this laptop between work and home, which are both WPA-PSK networks.  I also have a 'default' entry in my configs to connect to any open AP, and a static entry on my wired interface, because I sometimes use it as a portable server (ftp/http).  The wext driver was recommended, but I find madwifi seems to work just fine, as I was initially having problems drawing an IP.

Hope you don't mind me adding examples of my configs:

##### START /etc/network/interfaces #####
# The loopback network interface
auto lo
iface lo inet loopback

# The wired network interface
#allow-hotplug eth0

iface eth0 inet static
address 192.168.2.2
netmask 255.255.255.0
gateway 192.168.2.1

# The wireless network interface
allow-hotplug ath0
iface ath0 inet manual
wpa-driver madwifi
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf

# Home wireless
iface Home inet dhcp

# Work wireless
iface Work inet dhcp

# Default wireless
iface default inet dhcp

##### END /etc/network/interfaces #####

##### START /etc/wpa_supplicant/wpa_supplicant.conf #####
ctrl_interface=/var/run/wpa_supplicant
ap_scan=1


# Home - WPA-PSK
network={
    ssid="Home_AP"
    id_str="Home"
    proto=WPA
    key_mgmt=WPA-PSK
    pairwise=TKIP
    psk="home_passphrase"
    priority=5
}


# Work - WPA-PSK
network={
    ssid="Work_AP"
    id_str="Work"
    proto=WPA
    key_mgmt=WPA-PSK
    pairwise=TKIP
    psk="work_passphrase"
    priority=4          
}


# Default . Open
network={
    ssid=ANY
    key_mgmt=NONE
    priority=2
}

##### END /etc/wpa_supplicant/wpa_supplicant.conf #####

Fairly simple to setup.  Hopefully this may help others wanting to use wpasupplicant's roaming feature, as I had a hard time finding any kind of howto, although the documentation at README.modes explains it rather well.

So far my experience with it has been iffy.  It works most of the time, but every once in a while the connection will die, and the only way I can get it back up is a reboot.  Restarting networking and ifplugd services don't seem to remedy it even.  It seems to stay connected to the AP, but will not take an IP again.  Not sure if this an ifplugd or wpasupplicant problem yet, but I believe one of those is causing the connection to go down.

Hopefully I'm not completely out of the scope of your howto with this, as it is geared toward the old version of wpasupplicant.  The newer wpasupplicant is much easier to get up and running.  Although I still consider myself an amateur linux user (using mostly Debian based distributions for 2+ years), I hope this info may help in some way.  Feel free to use any information I have included here however you wish, if at all.

Jesse Murphy