I think the CS Unplugged approach has a tremendous amount of potential, particularly with its intended audience (primary school). In my 3rd grade class in 1986, one day the teacher told us that she had a loaf of sliced bread in a bag, a jar of peanut butter, a jar of jam, and a knife. She asked each student to write, on a sheet of paper, instructions for making a PBJ sandwich. When all the students had finished, the teacher followed each set of instructions exactly as written. It was amazing and hilarious to see the literal interpretations. I remember it very clearly because I was one of the students who gave incomplete instructions, and it was a minor blow to my ego because I was one of the smart kids. It was also my first programming lesson.
For young students, simple activities like these (and other communication / language exercises like sentence diagramming) can have significant benefits later in their education. I don't think introductory CS education should be completely replaced by non-computer exercises, but it's no surprise that many HS students and college freshmen don't "get it" when the first thing they're exposed to is a pile of code.
About the PBJ exercise, last semester (I'm in grade 10 right now), we had to do the same thing in Chemistry, except for a lab. It was teach us to provide detailed instructions in the lab write-ups. Almost no one in the class had detailed enough instructions. It worked like a charm. After that, on the rest of my labs, I went in a lot of detail in the instructions. I have to agree that it is a great way of teaching, and it would be amazing if every student encountered it at least once in their schooling. Especially at a younger age, it would instill an attention to detail in the student, which would serve him well for the rest of his life.
For young students, simple activities like these (and other communication / language exercises like sentence diagramming) can have significant benefits later in their education. I don't think introductory CS education should be completely replaced by non-computer exercises, but it's no surprise that many HS students and college freshmen don't "get it" when the first thing they're exposed to is a pile of code.