I've been to the Marhaba Lounge in T1. I believe it also serves as the UAL lounge, so it can get busy as United has late night flights departing to the States. But, it's not so busy that you can't find a quiet little corner to get some work done.
They had a very nice buffet available. If you're a member of the Lounge Club, the Marhaba Lounge is part of their worldwide network.