Having just updated to the latest version of OS X, like many other people, I lost my wi-fi connection.
Following advice posted on the Apple forum here I managed to resolve the issue using these steps:
1. Went to System Preferences > Network and turned Airport off.
2. Deleted my Airport network connection.
3. Unplugged my router.
4. Went to Macintosh HD > Library > Preferences > SystemConfiguration folder and deleted com.apple.airport.preferences.plist and com.apple.network.identification.plist
5. Deleted the following from ~/Library/Preferences: com.apple.internetconfigpriv.plist and com.apple.internetconfig.plist.
6. Rebooted System and plugged router back in.
7. System Preferences > Network and added a new Airport network connection.
8. Clicked the Advanced button and added my (router) preferred network using WPA2 Personal with the password.
9. Turned Airport back on and was able to log in to my router configuration.
10. Changed wi-fi channel to 6.
This seemed to work for me, although I am yet to put my Mac back to sleep and leave it overnight. It certainly is an issue, and I repaired my permissions both before AND after installing the 10.6.5 Combo update. I did notice there were a LOT of permissions that were repaired after updating, mainly java-based.
This is not good enough Apple. Were it not for my iPhone and a 3G connection I would have been stuck finding a fix for this.Mac OSX Apple, OSX, preferences, settings