Something that has happened to me on retail is I look for an enchanter over trade chat and they tell me to meet them infront of the AH.
I go there, look for them, and cannot see them. We than have to group up inorder to complete the transaction. This is something that might occur in classic Phase 1.
Also, Blizzard needs to be transparent on exactly how big each layer is. If the cap for a new layer is 3000, what happens when the 3001st player logs in? Does he get his own layer to himself? Or do you just instantly teleport 1000 players from layer 1 to compensate? That would be strange.