How much is too much?

How much is too much? No, I am not talking about near-sighted attorneys suing the Red Cross. I am thinking in terms of screen space or "real estate." LCD screens rock and have become very reliable and economical. I have two 19" monitors at work and a 22" monitor at home. Recent studies, however, indicate that too much monitor real estate can actually decrease a person's productivity. And I completely agree with that. In today's super-charged environments of mandatory multi-tasking, how many things can we try to focus on before we lose focus (and our minds)?