Looks like Apple has another MacBook Air glitch to address, with multiple users complaining of the ultraportable's performance with the official USB Ethernet Adapter. According to a lengthy thread on the Apple support forum, use of the $29 adapter is proving haphazard at best: some users claim it will only work when connected via the notebook's right USB port, while others say it won't work at all. Instead, a location workaround appears to address the fault.
Some reports claim the adapter functioned briefly when plugged into the right hand port, but then failed to work after that, meanwhile, giving only the error message "Cable unplugged. Either the cable for USB Ethernet is not plugged in or the device at the other end is not responding." The same dongles are generally found to be fully functional when later hooked up to a MacBook or MacBook Pro, suggesting the adapter itself isn't at fault.
The solution - or at least temporary fix - appears to involve bypassing the "Automatic" location OS X assigns to the new connection when the USB Ethernet adapter is first plugged in. Deleting that and adding a new connection seemingly addresses the fault; we're guessing Apple will push out an update eventually that does this all automatically:
"Create a new location in the Network preferences. Plug the ethernet cord into the adapter, wait a second or two, then plug the adapter into the MBA. Open a page in Safari and keep refreshing it until it loads. It should recognize the adapter and get a network connection within a minute or two." anpwq, Apple Support Forum