Just an FYI, this was buried in a couple of other threads, I'm posting here to bubble it up to the top. Some machines don't reconnect to WiFi after waking from sleep if woken up via a keyboard. If you use the power button to wake from sleep, then the WiFi does reconnect. Pretty much all the details I have at the moment, my MacBook doesn't have the problem but my iMac does. EDIT: I'm marking this as resolved as the software update fixes the issue I was having. I'm aware that other people are still having some issues with WiFi, but this particular issue is now resolved.