The Wi-Fi on my brand new 2014 Mac Mini drops out 2 or 3 times per day. Even restarting doesn't fix it. This video describes the only solution I could figure out. After the fix, it works fine for five or ten more hours (as long as you're really close to your access point), then it drops out again.
TO FIX:
1. Turn off Wi-Fi
2. Forget All Wi-Fi Networks
3. Shut Down
4. Yank the Power Cord
Video quality sucks, sorry. I wanted to re-record with a less irritated voice but I returned the computer instead. Terrible experience.
Hope this helps someone.