Chris Spagnuolo has an interesting article on multitasking, The Myth of Managed Multi-tasking:
"You must always work not just within but below your means. If you can handle three elements, handle only two. If you can handle ten, then handle five. In that way the ones you do handle, you handle with more ease, more mastery and you create a feeling of strength in reserve."
He goes on to discuss the issue of multitasking from the perspective of people who are heavily embedded with technology, which has the effect of creating multitasking if you aren't careful.
I keyed onto the quote for another reason. One of the principles with the Theory of Constraints is that most systems are clogged with far too much work in process, creating all sorts of problems: slow turnaround, inflexibility, firefighting everywhere, etc. One of the early steps taken in many TOC implementations? Cut the active work. This has the effect that the remaining work is done faster AND with higher quality. (Paradoxically, most organizations see an increase in the amount of work completed over time.)