same happened on my Mac Book pro ( mid 2009 ) :-(
after the upgrade process and a post reboot, i couldn't get online with my WIFI connection anymore.
also plug in a network cable couldn't fix this issue. it seems like there are problems in getting an ip address.
the only way to FIX this problem is to restore the ( old ) /etc/authorization file.
i got an backup of this file in time machine and also in /etc/authorization~backup
after restoring the file ( from 10.7.2 or earlier ) and a reboot, everything works like a charm.
thanks to apple ( .. )