Wi-Fi turning on and off since Mavericks upgrade
Turns out there was a custom script running under a subdirectory of /Library/Scripts/ on this laptop. It looked something like this:

#!/bin/bash

dscacheutil -flushcache
if ifconfig en0 | grep inet;
then 
    /usr/sbin/networksetup -setairportpower en1 off
    /usr/sbin/networksetup -setairportpower en2 off
else
    /usr/sbin/networksetup -setairportpower en1 on
    /usr/sbin/networksetup -setairportpower en2 on
fi


Commenting its insides out fixed the problem The Wi-Fi no long periodically disconnects. I'm guessing that between 10.8 and 10.9, one of the commands in that script changed.