None of the solutions above worked for me...
if none of them work for you, try this. This solution worked for me.
I went into my com.apple.Boot.plist in /Extra/
and added this key
Then I deleted my network interfaces in Network System Prefs,
THEN deleted my .plist file in /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist
THEN i rebooted. and when I came back to LION I went into System Prefs / Networking and clicked the (+) and added my card.
what was different this time was it added "Ethernet" as "Ethernet" where before it was adding it at "Ethernet Device (en0)"
So i knew something had changed... sure enough, i run app store and BOOM! connected and able to download and purchase software.
I dit THIS in my GM setup, and it worked like a charm, many thanks