wifi 10.8.4
Seen lots of threads about people having problems connecting to or maintaining connection to WiFi following a 10.8.4 upgrade. I've had the problem now for two weeks but just managed to speak to Apple who talked me through clearning out the old System Configuration file, shutting down the Mac, holding down the power button (with power disconnected) for 15 seconds then rebooting and recreating connection to WiFi. This seems to have resolved the problem and internet connection is now faster than ever. Prior to this, I had already deleted all the available WiFi connections (in Network Preferences, Advanced, WiFi) and also deleted Keychain references to my networks in Go, Applications, Keychain Access, System.
iMac (27-inch, Late 2012), OS X Mountain Lion (10.8.4)