I am almost always more efficient when I am multitasking. I think for me it is because I am so ADD that f I am doing something that does not require 100% of my mental attention, I get distracted by anything and everything going on around me. But if I'm doing multiple things that don't require my full attention, then I can do them all better and quicker. I definitely find this at work. Hence why I spend so much time on gchat some days!