My Apple iMac Core Duo has been having constant Wi-Fi problems ever since upgrading to Apple's latest OS X 10.4.8. My Wi-Fi connection drops unexpectedly and refuses to come back until the system is rebooted. Even after a reboot, the Wi-Fi only returns after the access-point is manually re-selected.
Needless to say, this makes using the iMac completely unacceptable.
Interestedly, the MacBook Pro does not have the same problem.
Totally unacceptable lack of quality control, and not something I have come to expect from Apple.