When the Mac App store hangs on connection (10.6 or later)

1. Close App Store and iTunes completly (blue circle under each should disappear)
2. Open Terminal (Applications -> Utilities -> Terminal)
3. Run the following:
   

   mv -f ~/Library/Preferences/com.apple.storeagent.plist ~/Library/Preferences/com.apple.storeagent.old.plist
   mv -f ~/Library/Preferences/com.apple.appstore.plist ~/Library/Preferences/com.apple.appstore.old.plist
   

4. This will reset a number of preferences about the App Store.
5. Restart your Mac! - This is key!
6. Open App Store. you'll need to re-login