The research is almost unanimous, which is very rare in social science, and it says that people who chronically multitask show an enormous range of deficits. They’re basically terrible at all sorts of cognitive tasks, including multitasking.
So we have scales that allow us to divide up people into people who multitask all the time and people that rarely do, and the differences are remarkable. People who multitask all the time can’t filter out irrelevancy. They can’t manage a working memory. They’re chronically distracted.
They initiate much larger parts of their brain that are irrelevant to the task at hand. And even – they’re even terrible at multitasking. When we ask them to multitask, they’re actually worse at it. So they’re pretty much mental wrecks.
via The Myth Of Multitasking : NPR.
For your reading pleasure I’ve offered up just a few quotes from the transcript of a wonderful interview with Clifford Nass, author of “The Man Who Lied to His Laptop,” professor of communications at Stanford University. Listen to the entire interview. It is well worth your time.
lifeunderwriter.net 
I think it was from this interview but another quote I heard was, “It is healthy for the brain to do multiple integrative tasks at the same time. It is unhealthy for the brain to do multiple non-integrative things at the same time.” I would be interested to know how far this stretches.
I just checked the transcript and you are correct. The quote you provided is from the same interview. We are all interested to know how far this stretches. Unfortunately we won’t know until we get there. Thanks for your comment.