[T]he argument that multitasking on computers is bad because humans can't multitask is flawed. It uses the word "multitasking" in two different ways, but implies that the two kinds of multitasking are somehow the same thing. They're not: a task (or an app) on a computer, and a task performed by a human don't map to each other one-to-one. In fact, a single task performed by a human can easily make use of several applications running concurrently on a computer. […]
The fact that the iPad only lets me see one app at a time often does not help me focus. Instead, it forces me to switch between apps constantly, thus preventing me from focusing on my task. Every time I have to deal with the iPad's task switching, I'm interrupted.
I couldn't have made these points any more succinctly.