Not sure if Abu Dhabi still does it. It has, however, been an unmitigated disaster:
http://onemileatatime.boardingarea.com/2014/09/07/etihads-ab...
http://onemileatatime.boardingarea.com/2014/09/07/etihads-ab...
What sounds really, really annoying is that there are no facilities whatsoever (save for a coffee kiosk) and that you can't even sit down until the gate opens.
Personally, I wouldn't know since I never flew via Abu Dhabi (let alone to the US).