I just finished building my 29er wider (30mm I think) light bicycle rims last night. Laced them to DT Swiss 350 hubs with DT swiss competition spokes and DT brass nipples. All I did was prepare the thread end of the spokes with a little grease as you normally would.
I tried some nipple washers but they wouldn't fit through the holes on the internal skin of the rim. As I understand it these aren't required anyway. The holes are drilled in the center not off set by the way.
I found them very easy rims to work with. Built tension slowly and hardly took any truing. In fact they were a pleasure to work with compared to the other alu rims I have built.