Last night, for no apparent reason, I suddenly lost the WiFi connection on the iMac. I was unable to access the Internet or the other machines on my home network. Every attempt to reconnect to the network gave me an error message. My other laptop with WiFi was working fine, so I assumed it must be an iMac problem, but I tried re-booting the wireless router anyway. No help.
So I re-booted the Mac, hoping that would fix it. Nope: still unable to connect.
I tried re-booting a couple more times, along with various other acts of desperation. What finally fixed it was a full shutdown and restart. After that, everything was fine.
I'm finding that I have to reboot or shutdown-and-restart my iMac a lot more often than I do with my Windows box. I'm hoping that trend will change once I get through the initial shakedown period.