Today  I got the USB to Ethernet adapter for the MacBook Air from the Apple store.
At first it is not recognized by OSX (it seems that it is a problem for Kalyway and iDeneb – and probably others too) as there are two kexts missing (AppleUSBEthernet.kext and AppleUSBGigEthernet.kext).
I found this information on the invaluable Insanely Mac Forum.
You can get them here and install with Kext Helper and after that it works like a charm.