The folks at Realization, makers of the CCPM software Concerto, post newsletters and articles on topics related to Critical Chain from time to time. There’s No Such Thing as Good Multitasking one talks about the classic problem of multitasking and somehow people think there is "good" or "bad" multitasking. (I even talk about "bad multitasking", as this comes from older CCPM discussions.)
I love this anecdote:
The chief engineer from one of our clients kept track of every time he interrupted his first-line managers during one day. It got so bad, that by about 2 p.m., when he had already interrupted his managers more than 20 times, he felt too guilty to interrupt them again, and instead collected a list to be discussed in the next morning's meeting.
It is often not enough for individuals to say "no multitasking". They may not control the incoming requests - but their managers? How much control do they exert over this process? In these kinds of implementations, we often find the sources of interruptions and requests coming from exactly the people who want their people to "work smarter, not harder."
So, what to do? Seeing the problem is a big portion of this. The anecdote above had the manager listing all his interruptions. Other teams use CCPM tools to list out their tasks to provide focus - focus on the task with the most buffer consumption for which they have responsibility. Other groups go simple: use white board and sticky-notes to show the work and decide where to focus.