I think that in many cases the act of writing does help in the act of understanding and learning so there is a value to taking notes (which is also a problem when there are powerpoint handouts - particularly when the teacher basically just reads the slides).

For me, I seem to retain more when hand writing notes unless I focus on the note taking when typing on the computer.

The computer is also an inferior device for note taking in terms of annotations, images, equations etc. although that might not always be true.

Another point to consider is "does the kid type?" If a student has to think about the keys they're hitting it takes focus away from the material. This might sound silly but when we write by hand, we just write we don't think about the letters.

Finally, we have the distraction component. Not only for the kids with the computer who may or may not be distracted but also for the kids neighbors.

At the end of the day, Gypsy Spellweaver got it just right by saying "Studies can show trends. Students are not trends; they are individuals." - this is my problem with most education "research" (intentionally in quotes). It's really a case by case thing. There have been classes where I've had to ask students not to take notes on computer but many more where it's worked well.