After upgrading to 9.04 I have had poor performance using theWLAN on my laptop. It roams to my AP but I can hardly transfer data, sometimes I get a few seconds connection and then it's dropped. dmesg shows a lot of PHY transmission errors. I have a BCM4306 rev 02 network card. I think I may have found the solution today. I still get PHY transmission errors but surfing works much better than before. Time will show whether it is just a temporary fix or if it does in fact solve the problem.
I first ran sudo /usr/share/b43-fwcutter/install_bcm43xx_firmware.sh to download the latest firmware. I found (online) that this was perhaps not done in 9.04 and is the source for some user's problems. I rebooted the laptop but my problems remained.
I then went to System->Administration->Hardware Drivers and chose the B43 driver. I de-installed it (while connected to the LAN with cable) and then re-installed it. The latest driver was downloaded and installed.
I still see the PHY transmission errors in the log, but the connection does work better. Other people have reported that as an error - but as long as the connection works well I do not mind the error messages .. for now.