I've been having some problems with the Duplicator lately, such as:
Multi-Cubic selection is no longer working as it did, it's now stud-by stud when it took the dimensions of the brick you clicked before. This is kinda annoying for me as I don't think constantly switching back and forth from Cubic to Stack is good.
Also, I've noticed in the past that using the Duplicator then switching to certain tools (Paint Can, Hammer (?)) doesn't make them show up.
Nonetheless, I still think this is a nice tool.