Mac OS X 10.4.8: AirPort does not auto-connect to existing networks after restart or wake from sleep is NOT the bug I just had after installing the recent AirPort sercurity patches.
I couldn't connect with my 10.3.9 802.11b iBook to my WLAN. The connect icon was black, but all tcp/ip services were unavailable. Shut down / restart didn't fix anything.
I had to switch from non-Admin to an Admin account and get the 'keychain updated dialog'. Then I switched back to my regular account and this time it showed the 'keychain updated' dialog. Then it worked.
A relatively minor bug with this update, but it would have flummoxed most users.