Ok I installed ML today. Everything is OK except network. I've deleted and installed so many kext files (Rtl81xx, ionetworking, iouserethernet etc.) but no use.
While using 10.7.2, startup -v was showing the mac address of my ethernet and usb wifi and everything was OK.
I've also used my old kext files from 10.7.2 but no use again.
Edit: I've noticed something weird. When I check the devices under "About This Mac", the ethernet card shows up, but when I try to add it under System Preferences - Network, there is no option as Ethernet interface.