On Friday, Apple released iMac Wi-Fi Update 1.0, a small 1.3 MB update that is recommended for all iMacs (late 2009 and newer) running OS X 10.7.3. This appears to be a very specific update to resolve a very specific issue -- there's no other word from Apple on additional issues with iMac Wi-Fi that may have been occurring. You will have to reboot after installing the patch. The update is available through Software Update and can also be downloaded from the page linked below: iMac Wi-Fi Update 1.0