MacBook Wireless Problems Caused by 10.5.8 Update

Problem:

Built-in wireless on MacBook (and possibly MacBook Pro) is unable to connect to any wireless devices following an update to OS X (10.5.8 -- released Aug 5, 2009)

Connection issues include not being able to connect to a wireless network ("Connection Timeout") and high amounts of packet loss.

Solution:

Apple released a patch to fix this issue, just run software update (in System Preferences) and make sure you install the package that is like "AirPort performance while on battery power". This will undo the bug they introduced in the 10.5.8.

That did it for me.