I've also got this problem.
I live in another house then the actual access point, but before the upgrade there were no problems with the connection. Even though i'm inside the house i have problem, there's a 20-30% packet loss, even though i've got 90% signal strength.
Even though it worked perfect before the upgrade i've done some investigation of the network. I found an old thread on macosxhints.com[0] were alot of people had problems with d-link routers. I'm using a netgear wgr614v7, but some of the hints in the thread actually help. Changing the router to run in 802.11g mode only made the connection when i'm in the main house much better. But on the other hand i don't get a signal at all out in my house.
I've also made sure that there are no other wireless networks on the same channel as mine. There are 2-3 other networks but they're using channel 1 and 11 (mine is as 6). There hasn't been added any new equipment in the house that could interfere with the wlan.
So, to summarize, i started getting problems after the upgrade. Just minutes before when i was running "tiger" it was all good.
AirPort Card Information:
Wireless Card Type: AirPort Extreme
Wireless Card Locale: Worldwide
Wireless Card Firmware Version: 1.2.2
[0]
http://forums.macosxhints.com/showthread.php?t=61200
Message was edited by: mgor
Forgot the URL