I've just installed a minimal Ubuntu 11.04 image on a BeagleBoard-xM rev. B as described here: http://elinux.org/BeagleBoardUbuntu#Demo_Image (ubuntu-11.04-r1-minimal-armel.tar.xz).
I had no problems configuring WiFi (WPA-PSK, TKIP) using the drivers (rt2x00usb) provided for my Linksys WUSB54GC usb dongle. The connection works, but is unreliable. Usually I get 20-50ms ping to my local Access Point and a 20% packet loss rate. At the nearby PC the ping is 10 times smaller and I loose no packets (Ubuntu 10.04, the same WUSB54GC). Controlling beagleboard via ssh is very hard, as the lag is high and I have to wait a couple of seconds before I can see what I've typed.
Is there a solution to this problem? Different drivers maybe?