Wifi doesn't stay connected with 2010 MacBook Pro after upgrade to Mountain Lion
The only solution I found that actually worked was to replace the Mountain Lion Wi-Fi drivers with the ones included in Snow Leopard.

NOTE: This solution is not for the faint of heart and please ensure you've backed up your system - at worst this should only bork your Wi-Fi (which I'm assuming is already broken if you're trying these steps) but it's better to be safe than sorry.

Insert the Snow Leopard DVD into your DVD drive.

Open a Terminal:

sudo -s
cd /System/Library/Extensions
mv IO80211Family.kext /Users/&lt;your acct&gt;/Desktop 
cp -R /Volumes/Mac\ OS\ X\ Install\ DVD/System/Library/Extensions/IO80211Family.kext .


Run Disk Utility and Repair Disk Permission on your system drive

Rebuild the kext cache:

sudo touch /System/Library/Extensions


Wait a few minutes to ensure that the cache has been regenerated and then reboot.