The idea of 'multitasking' is a foolish thing, and I think most people have discovered now that to be successful at any task you need to focus without distractions. Singletasking is much more productive than multitasking. I might even argue that multitasking isn't possible, since humans can't switch context as fast as computers.
On the other hand, if you read the article in full, the debate isn't just about distractions and multi-tasking. Even when not being distracted, the use of a laptop to take notes is less effective than hand-writing notes. This is because laptops encourage a note-taking style where you don't necessarily need to actually process the information before typing it out:
> The researchers hypothesized that, because students can type faster than they can write, the lecturer’s words flowed right to the students’ typing fingers without stopping in their brains for substantive processing. Students writing by hand had to process and condense the spoken material simply to enable their pens to keep up with the lecture. Indeed, the notes of the laptop users more closely resembled transcripts than lecture summaries. The handwritten versions were more succinct but included the salient issues discussed in the lecture.
In another study[1], it was found that this happens even when students are warned against this "transcript" style of note-taking.
It all very much depends on the person doing the note taking, the information being taught, and the person doing the speaking, but in general it appears that laptops encourage bad note-taking and bad listening habits that hand-writing notes don't.
1: http://www.pbs.org/wgbh/nova/next/body/taking-notes-by-hand-...
Those are the same situations that encourage the "transcription" style of notes though, which as discussed above, presents its own problems. It's all about finding a balance.
You're assuming that the people using the laptop are multi-tasking but I don't know that that's necessarily true.