Earlier last week I asked PH whether people were more audio VS written feedback.
I was really surprised when I saw feedback in the form of audio as nearly as common as written feedback.
Of course the results from the form are not significative, but still - 6 for audio VS 7 for written.
I think it is a great way to create a more in-depth piece of feedback than text comments. It is also beneficial in order to give the presenter not only specific feedback, but also the tone and meaning behind your words. For example, when asking about a landing page roasting, if you ask me written feedback, I might omit to say that I skipped this and that sections.
That's my experience at least, and I believe a good reason why audio is so efficient.