Chapter 3 of Presentationzen talks about "going analog" as opposed to "going digital." The author says that you should step back from the computer when you are in the planning stage of a presentation. Try to make alone time for yourself so you can slow down your mind and think clearly. He also suggests you use pen and paper, whiteboards, and even sticky notes to jot down your ideas.
Personally, I prefer both pen/paper and the computer. Since I type faster than I write by hand, I usually use the computer to write down the words and sentences in my head before I forget it. Then there are times when I get stuck and I'm sitting at the computer for a while with nothing to say. That's when I find it best to step back from the computer and write things down on paper as ideas come to me. I find that even simple things like folding laundry will help me to clear my mind. It distracts me for a little while and when I come back to work on my project, I have a clearer mind.
Chris Zawadski who wrote "Paper vs. Computers: Which is Better to Write With?" thinks that you should use both. The author says "Our belief is that, just like the study about business professionals still relying on paper - both options should be utilized. They both have clear advantages. Some people do creative and rough work with pen and paper and then professional and share-able work with a computer and keyboard. No matter your process or personal preferences, we feel it's advantageous to take advantage of the benefits of both mediums!"
So, going back to the book, I do agree that we should step away from the computer when planning because it helps to keep your mind clear. As far as planning using only a paper/pencil, sticky notes, or whiteboard, I think it all depends on the individual.